Polysilazanes and related compositions, processes and uses

ABSTRACT

Silazanes and related compounds are prepared by (a) providing a precursor containing at least one Si-N bond, cleaving an Si-N bond in the precursor in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product with a second cleavage product or with a compound containing an Si-H bond, an N-H bond, or both, to produce an initial silazane product having at least one newly formed Si-N bond or (b) providing one or more reactants which contain an Si-H bond and an N-H bond, and causing reaction to occur between the two bonds in the presence of a transition metal catalyst to form an initial silazane product having newly formed Si-N bonds. Further products may result from additional reaction of either type. Novel compounds, including siloxazanes and high molecular weight polysilazanes, are provided. The compounds may be pyroloyzed to yield ceramic materials such as silicon nitride, silicon carbide and silicon oxynitride. In a preferred embodiment, substantially pure silicon nitride and articles prepared therefrom are provided. Fibers coatings, binders, and the like may be prepared from the novel materials.

ORIGIN OF INVENTION

The Government has certain rights in this invention as it was funded inPart under Contract Nos. N00014-84-C-0392 and N00014-85-C-0668 awardedby the Office of Naval Research.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.908,685, filed Mar. 4, 1986 (PCT/US86/00548), which is acontinuation-in-part of U.S. application Ser. No. 727,415, filed Apr.26, 1985, now issued as U.S. Pat. No. 4,612,383.

DESCRIPTION

1. Technical Field

The invention relates to the synthesis of compounds (by which it isintended to include monomers, oligomers and polymers) containing thestructure Si--N in the molecule. The invention concerns primarilylazanes and their derivatives, which may be pyrolyzed to yield a varietyof ceramic products, and also relates to siloxazanes (by which it ismeant monomers, oligomers and polymers containing the O--Si--N unit) andother compounds containing one or more Si--N bonds. The inventionadditionally relates to the synthesis of novel, high molecular weightpolysilazanes and their precursors, and the use of these uniquecompounds for the fabrication of ceramic coatings, fibers, binders, andinjection-molded articles. The invention also relates to the use ofpolysiloxazanes and polyhydridosiloxanes as ceramic precursors.

2. Background

Polysilazanes and their derivatives are useful among other things, forthe preparation of silicon nitride (Si₃ N₄, silicon carbide (SiC), Si₃N₄ /SiC alloys, Si₃ N₄ /carbon alloys, Si₃ N₄ /boron nitride alloys, andmixtures thereof. These ceramic materials can be used as structuralmaterials, protective coatings, and electronic materials because oftheir hardness, strength, structural stability under extremeenvironmental conditions and their wide variety of electronicproperties. In particular, these materials can be formed into ceramicfibers of value for reinforcement of composite materials. See, forexample, (a) Department of Defense Proceedings, Fourth Metal MatrixComposites Technical Conference, May 19-21, 1981, prepared for DOD MetalMatrix Composites Information Analysis Center; and (b) J. J. Brennan,"Program to Study SiC Fiber-Reinforced Matrix Composites", Annual Reportto Dept. of Navy (Nov. 1980), Contract No. N00014-78-C-0503.

Historically, polysilazanes were first synthesized by Stock et al almost60 years ago (see, e.g., Stock, A. and K. Somieski, Ber. Dtsch. Chem.Ges. 54:740 (1921)) via a simple ammonolysis technique (Scheme I).However, this ##STR1## approach usually produces mixtures of cyclomerswhere x is 3 to 5 that are obtained as the major products and smallamounts of linear oligomers where y is less than or equal to about 10.Because of their low molecular weight, however, these linearoligosilazanes are too volatile to be used as preceramic materials.

In order to obtain higher molecular weight, nonvolatile materials, itwas necessary to promote cross-linking reactions. In this manner,moderate molecular weight polysilazanes have been synthesized using avariety of techniques. See, e.g., Kruger, C. R. and E. G. Rochow, J.Polymer Sci. 2A:3179-3189 (1964). Rochow et al. discovered that ammoniumchloride catalyzes cross-linking in simple oligodimethylsilazanes toform polysilazanes (Scheme II) which ##STR2## were proposed to containcyclic monomer units cross-linked through nitrogen as suggested by thestructure of Formula 1. ##STR3##

The Penn et al. work follows up on U.S. Pat. Nos. 3,853,567 to Verbeekand 3,892,583 to Winter et al., wherein a high temperatureelimination/condensation reaction was shown to lead to soluble, highlycross-linked polymers as shown in Scheme III. Pyrolysis at hightemperatures provides ceramic ##STR4## yields of 60% with a mixture ofSi₃ N₄ and SiC ceramic materials.

A related cross-linking approach described, inter alia, in U.S. Pat.Nos. 4,312,970, 4,340,619, 4,535,007 and 4,543,344 begins with thepreparation of tractable polysilazanes having Me₃ Si groups linked tothe polymer backbone (Scheme IV) with the highest molecular weightsreported in the available literature, i.e. about Mw˜15,000 D andMz˜39,000 D: ##STR5## Ceramic yields obtained from pyrolysis fibersformed from this polymer are on the order of 45-55% with compositions of96% Si₃ N₄, 2% carbon and 2% oxygen after curing.

U.S. Pat. No. 4,482,669 to Seyferth et al. discloses that it is possibleto cross-link low molecular weight cyclic oligomers containing Si--Hbonds adjacent to N--H bonds via the following reaction: ##STR6## The NHbond is catalytically activated by the strong base in this reaction.This type of cross-linking generates two-dimensional polymers, thesolubility of which is limited by their sheet-like character. Ceramicyields of these materials are often quite high, up to about 86%, andtypically provides Si₃ N₄, SiC and carbon in a mole ratio of0.88:1.27:0.75. If the pyrolysis is carried out in an NH₃ atmosphere,then the only product is Si₃ N₄ with the other products remaining asslight impurities.

Zoeckler and Laine in J. Org. Chem. (1983) 48:2539-2541 describe thecatalytic activation of the Si--N bond and in particular the ringopening of octamethylcyclotetrasilazane and polymerization of thering-opened intermediate. Chain termination is effected by introducing[(CH₃)₃ Si]₂ NH as a coreactant giving rise to polymers (CH₃)₃Si--[NHSi(CH₃)₂ ]₂ --NHSi(CH₃)₃ where n may be 1 to 12 or more dependingupon the ratio of the chain terminator to the cyclic silazane. Thecatalyst used was Ru₃ (CO)₁₂. Other publications are as follows: W.Fink, Helv. Chem. Acta., 49:1408 (1966); Belgian Patent 665774 (1965);Netherlands Patent 6,507,996 (1965); D. Y. Zhinkis et al., Rus. Chem.Rev., 49:2814 (1980); K. A. Andrianov et al., Dok Akad. Nauk. SSSR,227:352 (1976); Dok Akad. Nauk. SSSR 223;347 (1975); L. H. Sommer etal., JACS 91:7061 (1969); L. H. Sommer, J. Org. Chem. 32:2470 (1969); L.H. Sommer, J. Org. Chem. 32:2470 (1967); L. H. Sommer et al., JACS89:5797 (1967).

In general, control of the polysilazane molecular weight, structuralcomposition and viscoelastic properties play a considerable role indetermining the tractability (solubility, meltability or malleability)of the polymer, the ceramic yield, and the selectivity for specificceramic products. In particular, the tractability plays a major role inhow useful the polymer is as a binder, or for forming shapes, coatings,spinning fibers and the like. The more cross-linked a polymer is, theless control one has of its viscoelastic properties. Thus, highlycross-linked and low molecular weight polymers are not particularlyuseful for spinning fibers because the spun preceramic fiber often lackstensile strength and is therefore unable to support its own weight. Bycontrast, high molecular weight, substantially linear polymers asprovided herein are extremely important. Such polymers represent asignificant advance in the art, as they provide chain entanglementinteractions in the fiber-spinning process and thus enhance the overalltensile strength of the spun fibers.

An example of how molecular weight correlates with the properties of aparticular polysilazane can be illustrated by the properties of --H₂SiNMe]_(x). The original synthesis of this material was reported bySeyferth et al. in Ultrastructure Processing of Ceramics, Glasses andComposites, Ed. Hench et al. (Wiley & Sons, 1984) via an aminolysisreaction: ##STR7## This method of preparation gives a mixture of avolatile cyclotetramer (35%) and nonvolatile oligomers. This mixture hasan Mn of about 330 D and gives only a 28% ceramic yield upon pyrolysis.Distillation of the volatile cyclomer yields 65% of low molecular weightnonvolatile oligomer (Mn=560) which is pyrolyzed to give a 39% ceramicyield. An improved method of preparing these oligomers is illustrated byScheme VII: ##STR8##

By the method of this invention, working at temperatures of lower thanabout 0° C. provides mostly nonvolatile linear oligomers (between about85% and 95%) that require no distillation/purification step. For thisproduct, the Mn is about 800-1,100 D (n˜14-19). Pyrolysis of thisimproved oligomer gives significantly higher ceramic yields of 50% withsome improvement in product quality, with Si₃ N₄ purities of above about80%, the remainder being carbon.

By the method of this invention, the silazane product of Scheme VII canbe further polymerized to give novel polymers with Mn greater than about10,000 D, in some cases greater than about 20,000 D, Mw greater thanabout 16,000 D and in some cases greater than about 32,000 D, Mz greaterthan about 40,000 D and in some cases greater than 80,000 D, or withobservable species having a molecular weight of higher than about 50,000and in some cases higher than about 500,000 D. Molecular weights as highas 2,500,000 D (see Example 23) have been detected for the polysilazanesas provided herein. Pyrolysis of these true polymer species will givesignificantly higher ceramic yields than previously obtained, theceramic yield to a large extent depending on the molecular weightdistribution and the polymer processing. Si₃ N₄ purities of 80% orhigher may be obtained, depending on the reaction conditions.

These novel high molecular weight polymers are soluble, exhibit a highdegree of linearity and give higher ceramic yields and Si₃ N₄ puritiesthan the oligomeric starting material. In addition, the viscoelasticproperties of the novel compounds can be carefully controlled using themethod of this invention. In particular, at higher molecular weights,these polymers exhibit non-Newtonian viscoelastic properties, allowingfor chain entanglement which will increase the tensile strength requiredto draw the thin precursor fibers required to form ceramic fibers.

The high ceramic yields are of considerable value in binderapplications, injection molded parts and in matrix applications. Duringpyrolysis the density/volume change from preceramic polymer (1-1.3 g/cc)to ceramic (3.2 g/cc for Si₃ N₄) can be significant. Thus, ceramicyields far below theoretical will only magnify the resultingdensity/volume change. For example, a 50% ceramic yield for a Si₃ N₄precursor of density 1.0 will result in a final decrease in volume ofapproximately 80%.

It should be noted that certain aspects of the present invention arediscussed in co-pending application PCT/US86/00548, U.S. Ser. No.908,685, filed Mar. 4, 1986, and the parent thereto, U.S. applicationSer. No. 727,415, filed Apr. 26, 1985, now issued as U.S. Pat. No.4,612,383. The disclosures of these related cases are herebyincorporated by reference in their entirety.

DISCLOSURE OF THE INVENTION

It is thus a primary object of the present invention to overcome theaforementioned disadvantages of the prior art.

It is another object of the invention to provide improved methods ofpreparing silazanes, and, in particular, high molecular weightpolysilazanes.

It is still another object to provide methods of preparing siloxazanesand high molecular weight polysiloxazanes.

Still another object of the invention is to provide a method of makingsilazanes and related compounds using transition metal catalysts whichprovide an extremely rapid initial reaction rate.

A further object of the invention is to provide novel compoundsincluding siloxazanes and high molecular weight polysilazanes andpolysiloxazanes.

Still a further object of the invention is to provide a method of makingceramic materials having a high silicon nitride content, and to prepareand pyrolyze precursors to silicon oxynitride and silicon carbide finepowders.

Another object of the invention is to provide a method of pyrolyzingpreceramic materials so as to control the ceramic yield obtained, e.g.by controlling temperature, temperature ramping, pressure, theparticular gaseous atmosphere selected, etc.

Still another object of the invention is to provide a method of coatingsubstrates with ceramic materials.

Other objects of the invention include methods of making fibers, fine ormonodispersed powders, coatings, porous articles such as ceramic foams,filters and membranes, and compression-molded and injection-moldedarticles using, inter alia, the preceramic polymers and the ceramicmaterials as provided herein.

Still other objects of the invention include methods of using thepolymers of the invention as binders, as adhesives, in infiltrationapplications, and in matrix and composite materials.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art on examination of thefollowing, or may be learned by practice of the invention.

In one aspect of the invention, a monomeric, oligomeric or polymericprecursor containing at least one Si--N bond is provided. An Si--N bondin the precursor is cleaved in the presence of hydrogen or a hydrogendonor, and the cleavage product is reacted with another cleavage productor with a compound containing an Si--H bond, an N--H bond, or both, inthe presence of a transition metal catalyst. The initial silazaneproduct so formed has at least one newly formed Si--N bond.

In another aspect of the invention, one or more reactants are providedhaving an Si--H and an N--H bond, and reaction is caused to occur so asto form hydrogen and a silazane product having at least one newly formedSi--N bond and at least two Si--N bonds in its structure.

Reaction of one type may be caused to follow reaction of the other type;alternatively, both types may be caused to proceed simultaneously, forexample, if one or more starting materials are provided having incombination Si--N, Si--H and N--H bonds. Thus, a variety of reactionproducts can be prepared with these processes.

The silazane products may be provided as preceramic polymers havingmoderate or very high molecular weight, which polymers in turn provide acorrespondingly high ceramic yield upon pyrolysis. As will be discussedbelow, these high molecular weight polymers may be produced in such away so as to provide substantially pure silicon nitride upon pyrolysis.

In a preferred embodiment of the invention, the catalysts which are usedin the above-described reactions provide rapid reaction rates, on theorder of about fifteen to fifty times faster than reactions employingstandard catalysts.

The invention also encompasses novel silazane and siloxazane compoundsand a variety of applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the GPC results of a silazane ([H₂ SiNMe]_(x)polymerization catalyzed by Ru₃ (CO)₁₂ ;

FIG. 2 graphically represents TGA pyrolysis of a polysilazane atdifferent temperature ramping rates;

FIG. 3 is an SEM photograph of a formed Si₃ N₄ /polysilazane body afterheating to 800° C. in N₂ ; and

FIG. 4 is an SEM photograph of a formed Si₃ N₄ /polysilazane body afterheating to 1725° C. in N₂.

MODES FOR CARRYING OUT THE INVENTION

"Silazanes" as used herein are compounds which contain one or moresilicon-nitrogen bonds. The term "polysilazane" is intended to includeoligomeric and polymeric silazanes, i.e. compounds which include two ormore monomeric silazane units.

"Siloxazanes" as used herein are compounds which contain the unit[O--Si--N]. The term "polysiloxazane" is intended to include oligomericand polymeric siloxazanes, i.e. compounds which include two or moremonomeric siloxazane units.

"High molecular weight" polymers as provided herein are polymers thathave an Mn greater than about 10,000 D, in some cases greater than about20,000 D, Mw greater than about 16 000 D and in some cases greater thanabout 32,000 D, Mz greater than about 40,000 D and in some cases greaterthan 80,000 D, or with observable species having a molecular weighthigher than about 50,000 D and in some cases greater than 500,000 D.

"Mn", "Mw" and "Mz" are defined as follows. The number average molecularweight Mn of a polymer distribution is given by ##EQU1## the weightaverage molecular weight Mw of a polymer distribution is given by##EQU2## and the Mz value is given by ##EQU3## wherein Wi is the weightof each individual polymeric or oligomeric species, Ni is the number ofindividual species in the distribution, and Mi is the mass fraction ofeach individual species. Where not otherwise specified, molecularweights for a particular polymer distribution obtained directly will begiven as calculated prior to any separation or distillation step.

"Substantially linear" oligomers or polymers are noncyclic structureshaving two or more monomeric units and which are not extensivelycross-linked or branched.

A "substantially pure" ceramic material is intended to mean a ceramicmaterial comprising at least about 75 wt. % of a particular compound.

The "ceramic yield" of a compound upon pyrolysis indicates the ratio ofthe weight of the ceramic product after pyrolysis to the weight of thecompound before pyrolysis.

The "purity" of a particular compound in a mixture of ceramic materialsis defined as the weight percent of that compound in the mixture.

"Cyclic silazanes" are cyclic compounds having one or more Si--N bondsin the molecule.

"Silyl," unless otherwise specified, includes siloxyl, siloxazyl andsilazyl.

Silazane and siloxazane "copolymers" incorporate more than one type ofmonomer unit defined as a precursor or reactant in reactions of type (a)or type (b) herein.

A "tractable" polymer is one which is meltable, soluble or malleable orwhich can be processed like an organic polymer to form a desired shape.

The compounds provided by the processes of the present invention aremonomeric, oligomeric or polymeric structures having one or more newlyformed Si--N bonds. The reactions which form these structures may bebroadly grouped into two types.

In the reaction which will sometimes hereinafter be referred to as thetype (a) reaction, a precursor is initially provided which contains atleast one Si--N bond. Cleavage of an Si--N bond in the precursor iscatalytically effected in the presence of hydrogen or a hydrogen donor,and the cleavage product is then caused to react with a second cleavageproduct or with a compound containing an Si--H bond, an N--H bond, orboth, to produce an initial silazane product having at least one newlyformed Si--N bond.

In what will sometimes hereinafter be referred to as the type (b)reaction, one or more reactants are provided which in combinationcontain an Si--H bond and an N--H bond, and reaction is caused to occurbetween the two bonds in the presence of a transition metal catalyst,whereby an initial silazane product is provided having at least twoSi--N bonds, at least one of which is newly formed.

The "initial" silazane products so provided may be caused to reactfurther, according to either the type (a) or type (b) reactions, orboth, simultaneously or sequentially. These reactions may includereaction with other M--H bonds where M is, for example, B, Al, Ga, In,Ge, Pb, S, or Sn.

A. Preparation of Precursor Materials

The precursor material may be monomeric, oligomeric or polymeric, and,in addition to at least one Si--N and/or Si--H bond, may contain one ormore Si--Si, Si--C, Si--O, or N--H bonds. Ultimately, an Si--N bond orSi--H bond and, in some cases, one or more of the "Si--A" bonds of theseprecursors, wherein A is Si, C or O will be caused to break and one ormore new Si--N bonds are caused to form. In general, precursors havingSi--N, Si--H bonds or both are illustrated by Formulae 2 and 3: ##STR9##

In the above formulae, x is an integer from 0 to 4 inclusive y is aninteger from 0 to 4 inclusive, z is an integer from 0 to 2 inclusive,the sum of x, y and z is 4, a is an integer from 0 to 2 inclusive, b isan integer from 0 to 2 inclusive, the sum of a and b is 2, and m is aninteger defining the number of monomer units in the oligomer, polymer orcopolymer. The R moieties, i.e. the substituents on the nitrogenatom(s), which may be the same or different and may form part of acyclic or polymeric structure, are independently selected from the groupconsisting of: hydrogen; boryl; hydrocarbyl including lower alkyl(1-6C), lower alkenyl (1-6C), lower alkynyl (1-6C), aryl includingphenyl, benzyl and the like, lower alkyl substituted aryl,cycloaliphatic; silyl or polysilyl, including silazane, siloxane, andsiloxazane groups (hereinafter sometimes "silazyl", "siloxyl", and"siloxazyl"); said hydrocarbyl and said silyl functionalities beingoptionally substituted with amino, hydroxyl, an ether moiety or an estermoiety, lower alkoxy (1-6C), a fused aromatic radical of 8 to 20 carbonatoms, or an organometallic radical which may include elements such asB, Al, Ga, In, Ge, Pb, S, or Sn. The nitrogen may also be present invarious forms such as --NH--, --NH--NH--, --NH--NR--, --NR--NR--,--NR--R--NR-- , polyamines, and the like.

The R' groups, i.e. the substituents on the silicon atom, which may bethe same or different and may form part of a cyclic or polymericstructure, are independently selected from the group consisting of:hydrogen; amino; hydrocarbyl including lower alkyl (1-6C), lower alkoxy(1-6C), lower alkenyl (1-6C), lower alkynyl (1-6C), aryl includingphenyl, benzyl and the like, lower alkyl substituted aryl,cycloaliphatic; silyl or polysilyl including silazyl, siloxyl, andsiloxazyl; said hydrocarbyl or silyl being optionally substituted withamino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, afused aromatic radical of 8 to 20 carbon atoms, or an organometallicradical which may include elements such as B, Al, Ga, In, Ge, Pb, S, orSn. The silicon moiety, as above, may be present in various forms, i.e.as --SiR'₃, --SiR'₂ --, --SiR'₂ --SiR'₂ --, polysilane, etc. Although R'may in some instances be a hydrocarbyl moiety, it is preferable for manyapplications that the precursor be substantially free of Si--C bonds,e.g., for the ultimate preparation of ceramic products which aresubstantially carbon-free.

These precursors or reactants are preferably prepared by methods as willbe described and claimed herein.

Scheme VIII illustrates a preferred synthetic route used in making amonomeric precursor useful in the present method. ##STR10## In the abovereaction sequence, X is a halogen substituent, preferably chloride, andthe R moiety are as set forth above.

Procedurally, the halogen-substituted silane H₂ SiX₂ is provided in asolvent, preferably a polar solvent such as tetrahydrofuran, diethylether, and the like, and approximately four equivalents of thedi-substituted amine are gradually added. The temperature during thisaddition and admixture step is low, preferably maintained between about5° C. and -30° C. The reaction mixture is slowly allowed to warm, andthe aminosilane "precursor" product is isolated by any known method,e.g. by filtration and subsequent extraction.

Scheme IX illustrates the preferred method of making oligomeric orpolymeric precursors containing Si--N bonds. ##STR11## The reaction ofScheme IX involves preparation of oligomers or polymers fromhalogen-substituted silanes and mono-substituted amines, X and R beingdefined as above for the compounds of Scheme VIII. (See Examples 1-3.)Use of the mono-substituted rather than the di-substituted amineprovides an oligomeric or polymeric product rather than a monomericspecies. Procedurally, the reaction is carried out as described for themonomer preparation reaction of Scheme III. Approximately threeequivalents of mono-substituted amine are needed to complete thereaction (a ratio of between about 2.7:1 and 3.3:1 of RNH₂ :H₂ SiX₂ ispreferred to obtain higher molecular weights). In a modified process, anexcess of amine base containing no N--H bonds, e.g. triethylamine, maybe added to neutralize the HCl formed during the reaction, in whichcase, less of the mono-substituted amine is required (e.g., between0.9:1 and 1.1.:1 RNH₂ :1 Si--X bond). As in the reaction of Scheme VIII,a polar solvent is preferred here as well.

The compound represented by Formula 3 is a novel composition of matterwhere R'=H, NR₂ or NR-- with R as defined above, and m representing thenumber of monomer units in the polymeric or copolymeric structure; forR=CH₃, m being such that Mn is greater than about 600 D before anydistillation or separation of the product.

Modification of the oligomeric or polymeric precursor represented byFormula 3 may be carried out as follows, in order to provide a copolymerwhich in some instances may be preferred for further synthesis or forpyrolysis. An example of such a copolymer is represented by Formula 4:##STR12## One or more compounds of formula R¹ SiX₃ or SiX₄, where X ishalogen and R¹ is preferably H but may be lower alkyl (1-6C) or aryl,e.g., phenyl or benzyl, are added to the reaction mixture to controlcarbon content in the form of Si--C bonds. By control of the H₂ SiX₂ :R¹SiX₃ :SiX₄ mixture ratio, the Mn, Mw and Mz values can be increasedwhile maintaining tractability of the product as well as substantiallinearity. In addition, a higher fraction of amine reactant RNH₂ isincorporated into the copolymeric product. These additional aminemoieties may serve as latent reactive groups during pyrolysis. It shouldbe noted that substantially the same result may be achieved by replacinga portion of the amine reactant RNH₂ with ammonia in addition to orinstead of the RSiX₃ or SiX₄. Such a procedure, in conjunction withapplicants' basic method of synthesizing precursor species, as outlinedabove, represents an improvement over known methods insofar as themolecular weight of the product is concerned.

All oligomeric or polymeric precursors represented by Formula 3 may bepyrolyzed by themselves or may be further reacted catalyticallyaccording to the reactions of either type (a) or type (b).

Suitable precursor materials for further reaction of type (a) or type(b) or both thus include alkylamines such as monomethylamine,dimethylamine, monoethylamine, hydrazine and hydrazine derivatives,polyamines, and the like, as well as a variety of silanes, silazanes,polysilazanes, siloxanes, siloxazanes, and the like. These precursorsmay be modified by inclusion of additional latent reactive groups suchas hydrogen, amine, alkoxy, sulfide, alkenyl, alkynyl, etc., orcross-linked with suitable cross-linking reagents.

B. Formation of Silazanes

The aforementioned precursor or reactant materials may be used in eitherthe type (a) reactions, wherein an Si--N bond is cleaved and a new Si--Nbond is formed, or in type (b) reactions, wherein an Si--H moiety iscaused to react with an N--H moiety so as to form a compound having anewly formed Si--N bond. Either reaction is carried out catalytically,under suitable conditions as will be outlined below.

Catalysts suitable for carrying out subsequent reaction of theseprecursors or reactants according to reactions of either type (a) ortype (b) as described above are any type of transition metal catalystssuch as those indicated in Table I, below, which are homogeneouscatalysts that either dissolve in the reactants or in a solvent used todissolve the reactants. Heterogeneous catalysts such as those of TableII may also be used or mixtures of homogeneous catalysts and/orheterogeneous catalysts. (It should be pointed out here that the"homogeneous" and "heterogeneous" classifications are made herein on thebasis of solubility in organic solvents. However, it is not uncommonthat during the reactions, homogeneous catalysts may be converted into aheterogeneous form and vice versa.) These catalysts may include anynumber of ligands, including amino, silyl and organic ligands, asdiscussed below and as illustrated in Tables 1 and 2.

Preferred catalysts are transition metals, and in particular thetransition metals of Group VIII. Especially preferred catalysts arepalladium catalysts, e.g. of the formula Pd, PdX₂, L₂ PdX₂ or L₄ Pd,where X is an anionic species such as a halide, and L is a covalentligand, which may be organic, phosphine, arsine, amine, nitrile, and mayadditionally include silicon substituents. Examples are PdCl₂, Pd(OAc)₂,(φCN)₂ PdCl₂ and Pd/C. As demonstrated in Example 30, these catalystsprovide initial reaction rates on the order of fifteen to fifty timesfaster than that achieved with standard catalysts such as Ru₃ (CO)₁₂ andRh₆ (CO)₁₆ under the same conditions.

The catalyst(s) may be supported on a polymer, inorganic salt, carbon,or ceramic material or the like. The heterogeneous catalyst may beprovided in a designed shape, such as particles, porous plates, etc.

The catalyst can be activated by heating alone or by concurrenttreatment of the reaction medium with particulate or nonparticulateradiation. The catalyst may also be activated by promoters such asacids, bases, oxidants or hydrogen, or may be stabilized by reagentssuch as amines, phosphines, arsines and carbonyl. The concentration ofcatalyst will usually be less than or equal to about 5 mole % based onthe total number of moles of reactants, usually between about 0.1 and 5mole %. In some instances, however, catalyst concentration will be muchlower, on the order of ppm.

Table 1, Homogeneous Catalysts

H₄ Ru₄ (CO)₁₂, Fe(CO)₅, Rh₆ (CO)₁₆, Co₂ (CO)₈, (Ph₃ P)₂ Rh(CO)H, H₂PtCl₆, nickel cyclooctadiene, Os₃ (CO)₁₂, Ir₄ (CO)₁₂, (Ph₃ P)₂ Ir(CO)H,NiCl₂, Ni(OAc)₂, CP₂ TiCl₂, (Ph₃ P)₃ RhCl, H₂ Os₃ (CO)₁₀, Pd(Ph₃ P)₄,Fe₃ (CO)₁₂, Ru₃ (CO)₁₂, transition metal hydrides, transition metalsalts (e.g., ZnCl₂, RuCl₃, NaHRu₃ (CO)₁₁) and derivatives, PdCl₂,Pd(OAc)₂, (φCN)₂ PdCl₂, and mixtures thereof.

Table 2, Heterogeneous Catalysts

Pt/C, Pt/BaSO₄, Cr, Pd/C, Co/C, Pt black, Co black, Ru black, Ra--Ni, Pdblack, Ir/Al₂ O₃, Pt/SiO₂, Rh/TiO₂, Rh/La₂ O₃, Pd/Ag alloy, LaNi₅, PtO₂,and mixtures thereof.

The reaction is carried out in solution with the solvent comprisingeither the reactants themselves or an added nonreactive organic solventsuch as a hydrocarbon, an ether (e.g., ethyl ether, tetrahydrofuran), ahalogenated hydrocarbon (CHCl₃, CH₂ Cl₂, ClCHF₂, ClCH₂ CH₂ Cl, anaromatic such as benzene, toluene, or methylphenyl ether, or a polarsolvent such as acetonitrile, pyridine, or a tertiary amine. Somereactions may, if desired, be carried out in the gas phase by flowingthe reactant(s) over a metal catalyst.

Mild temperatures that will activate the catalyst are typically used.Such temperatures will normally be in the rang of -78° C. to 250° C.Higher temperatures are necessary especially where steric hindrance is aproblem. In general, higher temperatures provide for a faster reaction,but will result in a greater degree of cross-linking. Type (b) reactionsrequire a lower temperature than type (a) reactions, generally, ascleavage of the Si--N bond in the type (a) reactions requires a higheractivation energy.

Where the reaction is of type (a) (cleavage of an Si--N bond andformation of a new Si--N bond, i.e. rearrangement or metathesisreactions), the reaction is carried out in the presence of hydrogen or ahydrogen donor. Suitable hydrogen donors include silicon hydrides, metalhydrides optionally activated with a proton source, alcohols, amines,mono-, di- and tri-alkylamines, tetralin, tetrahydroquinoline, and thelike.

In type (a) reactions, the cleavage product reacts with a compoundcontaining an Si--H bond, an N--H bond, or both, to form an initialsilazane product having at least one newly formed Si--N bond. In type(b) reactions, one or more reactants which in combination contain anSi--H and an N--H bond are caused to react. In both of these reactions,the compound containing the N--H bond may be ammonia, RNH₂, R₂ NH, withR as defined above, for precursor compounds. One or more compoundscontaining an M--H bond may also be present, wherein M is, for example,B, Al, Ge, In, Ga, Pb, S, or Sn, which reacts with either the cleavageproduct of type (a) reactions or with a reactant in type (b) reactions.

In reactions of type (b), the Si--H and N--H bonds which are caused toreact may be in the same compound, causing cyclization orpolymerization, or they may be in two or more different compounds.

Examples of type (a) reactions thus include the following: ##STR13##Examples of type (b) reactions include: ##STR14##

After an initial reaction according to type (a) or type (b) (or both),further reaction of the initial silazane product(s) may result, by lapseof time, type of catalyst, amount of catalyst, choice of solvent,increase in temperature, or addition of further reactive species. Duringthe reaction process, or after completion thereof, the low and highmolecular weight fractions may be separated by size exclusionchromatography, ultrafiltration, membrane separation, distillation, orpartial precipitation techniques. Either fraction so obtained may berecycled through the type (a) or type (b) reaction sequence again. Forexample, the low molecular weight fraction can be further reacted so asto yield another crop of high molecular weight polymers.

A variation of the type (b) reaction is where ammonia is reacted with acompound of formula R₃ 'SiH, with R' as given above: ##STR15##

Polysilazanes prepared by the method of the present invention may beprovided as preceramic polymers having a molecular weight far higherthan that achieved by the prior art. Previously, tractable polysilazaneshaving molecular weights only as high as about Mn 10,000 D (Mw˜16,000 D,Mz˜40,000 D) were known, and these polymers displayed a number ofproblems with regard to volatility, purity, cross-linking, molecularstructure, carbon content, etc. By contrast, tractable polymericsilazanes having much higher molecular weights have been achieved withthe present method (see Example 23). Thus, the invention hereinencompasses compositions of matter having the recurring structure##STR16## wherein R and R' are as defined above for the nitrogen andsilicon substituents, respectively, wherein the polymer is tractable andwherein Mn is higher than about 10,000 D, preferably higher than 20,000D, the Mw is higher than about 16,000 D, preferably higher than about32,000 D, Mz is higher than about 40,000 D, preferably higher than about80,000 D or combinations thereof, and the overall polymer distributionprovided contains compounds with molecular weights greater than about50,000 D, preferably greater than about 500,000 D as observed by, e.g.,size exclusion chromatography. These Mn, Mw and Mz values are given forthe polymer distribution obtained directly without any separation ordistillation step. Polysilazanes containing the repeating unit [H₂SiNCH₃ ] in the polymer or the copolymer having Mn greater than about600 D before vacuum distillation of volatile compounds and greater thanabout 800 D after distillation or with Mw greater than 2000 D or Mzgreater than about 4000 D or combinations thereof are also newcompositions of matter. "N" and "Si" may represent polyamino orpolysilyl structures as outlined above.

The invention also encompasses novel silazane structures prepared by thereactions of type (a) and type (b) wherein a precursor or reactant hasat least one Si--N bond and an Si--H bond or an N--H bond or both, andthe reaction product has at least two different types of Si--N bondspecies, wherein an "Si--N bond species" (i.e., two nonidenticalstructures) is defined as an R'₃ Si--NR₂ moiety with R and R' as givenearlier. Novel compounds are also prepared by the reaction of silane ora mono-substituted silane (R'₃ SiH₃) with an NHR₂ compound.

The invention further includes novel siloxazane oligomers and polymerswhich include the structure R"----O--Si--N]. These can be prepared fromsiloxane precursors, i.e. precursors having one or more Si--O and two ormore Si--H bonds, according to the method outlined as type (b). Thefollowing scheme illustrates the various ways in which polysiloxazanesmay be prepared according to the method of the present invention.##STR17## Novel siloxanes as provided herein are of the generalstructure

    R"----O--Si--N]

wherein R" is silyl or hydrocarbyl. More specifically, novel siloxazanemonomers are of the structure ##STR18## wherein x is an integer from 2to 3 inclusive, y is an integer from 1 to 2 inclusive, z is an integerfrom 0 to 1 inclusive, R and R' are as given above and R" is in thiscase defined as R but excludes amino and alkoxy substituents. Novelpolysiloxazanes also include oligomeric and polymeric species, which aregiven by ##STR19## wherein a is an integer from 0 to 2 inclusive, b isan integer from 0 to 1 inclusive, the sum of a and b is 2, m is aninteger defining the number of monomer units in the compound, and R andR' are as given above. If desired, high molecular weightpolysiloxazanes, having Mn≧10,000 D, preferably ≧20,000 D, Mw≧16,000 D,preferably ≧32,000 D, or Mz≧40,000 D, preferably ≧80,000 D orcombinations thereof, may be obtained by the methods outlined above.Synthesis of these compounds is carried out according to the type (b)reaction sequence.

C. Pyrolysis to Ceramic Materials

Another important advantage of the compositions and methods of thepresent invention is the specificity and degree of ceramic yield uponpyrolysis. For example, the high molecular weight polysilazanes displaya correspondingly high ceramic yield, the ceramic materials so providedhaving a high silicon nitride content if desired. Silicon nitride may beprovided with purity higher than about 80% upon pyrolysis of thepolysilazanes provided herein when pyrolysis is conducted undernitrogen, argon or other inert atmosphere, or higher than about 95% uponpyrolysis of the polysilazanes in an ammonia or other amine atmosphere.Carbon-free polysilazanes which may be prepared according to the methodherein may provide silicon nitride of even higher purity, i.e. 98-99% orhigher.

Similarly, high ceramic yields of silicon oxynitride (Si₂ ON₂) mixturesmay be obtained upon pyrolysis using the methods described herein. Thenovel methods represent a significant advance in the art, as knownsynthetic procedures for making silicon oxynitride, a desirable ceramicmaterial having refractory properties of both oxides and nitrides, areproblematic. Two novel pathways for production of silicon oxynitride areprovided herein.

In the first of these, siloxane oligomers or polymers such as [CH₃SiHO]_(x) can be reacted with ammonia or amine to introduce nitrogenmoieties into these species (see, e.g., Schemes XIX-XXIII). Thesereactions can lead to the formation of a nitrogen cross-linked polymerhaving a homogeneous distribution of Si--O and Si--N bonds in thepolymer. The siloxazane so provided may be pyrolyzed under an inert gassuch as nitrogen or argon, or under ammonia or a gaseous amine compound,to yield ceramic mixtures containing silicon oxynitride.

Alternatively, nitrogen-free siloxane starting materials which may beoligomeric or polymeric are pyrolyzed under ammonia or a gaseous amineatmosphere to give silicon oxynitride directly. In this case, thenitrogen is introduced into the siloxane during rather than prior topyrolysis. The siloxane may be a sesquisiloxane ([R'SiO₁.5 ]_(n)), apolyhydridosiloxane (Formula 8) or a cross-linked polysiloxane (Formula9) or a polysiloxane with latent reactive groups (Formula 8) such ashydrogen amine, alkoxy, sulfide, alkenyl, alkynyl, etc., which can becross-linked during heating or replaced during curing. ##STR20##

In the above formulae, a, b, and R' are defined as for Formula 3.

If desired, silicon carbide, also, may be prepared in high yield uponpyrolysis, using polyhydridosiloxane-based preceramic polymers andselected pyrolysis conditions. The common method for production of SiCfine powder is a high temperature reaction between silica and carbonpowders, although more recently, SiC powders have been prepared bypyrolysis of sesquisiloxanes (see, e.g., Fox et al., "Better Ceramicsthrough Chemistry" Symposium, J. Brinker, Ed.; Mat. Res. Soc. (1986), inpress). The present method provides an inorganic polymer-controlledroute to silicon carbide fine powders and coatings which are morehomogeneous than previously obtained and a process by which thecomposition of the product and the amount of cross-linking therein canbe carefully controlled. This method decreases the oxygen content of thethe previous method in the polymeric precursor, leading to higher puritySiC powders.

The general procedure described above in type (b) reactions can be usedto prepare preceramic polyhydridosiloxanes, e.g. by cross-linkingsiloxane precursors with amines such as monoalkylamines, ammonia,hydrazine, and the like, using Si--H catalytic activation. Inalternative embodiments, other cross-linking agents such as water,diols, ethers, sulfides, alkenyl, alkynyl, and dienoic compounds may beused, as can organic substituents (e.g., lower alkyls) modified withlatent reactive groups such as amines, hydroxides, alkoxides, sulfides,ethers, etc., also using an Si--H catalytic activation method.

Procedurally pyrolysis, according to the preferred method of the presentinvention, is carried out as follows. A polysilazane, polysiloxazane orpolysiloxane is heated in an inert atmosphere such as in nitrogen orargon, or in an ammonia or amine atmosphere, at a predetermined heatingrate. As will be demonstrated in Examples 31 and 32, the heating rateduring pyrolysis is strongly correlated to the yield of ceramic materialobtained. Preferred heating rates for bulk pyrolysis are between about0.1° C. and 10.0° C. per minute, preferably between about 0.5° C. and2.0° C. per minute, with a particularly effective heating rate,optimizing ceramic yield, of about 0.5° C. per minute. In someapplications, however, flash pyrolysis may be preferred. The temperatureof the polymer is typically raised to between about 500° C. and about900° C., optionally higher, to about 1600° C.-1800° C., to providesintering or grain growth of the ceramic material. The heating processmay include one or more isothermal holding steps, in order to controlthe pyrolysis, to provide more cross-linking at moderate temperature(less than about 400° C.) and to further increase the yield of the finalproduct. If desired, pyrolysis may be carried out in the presence of acatalyst; examples of suitable catalysts are set forth in Tables I andII.

Optionally, pyrolysis may be carried out only partially, i.e. inapplications where it is not necessary to obtain a fully pyrolyzedmaterial. Such applications include coatings, siloxazane or silazanerubbers, glasses, etc., or where the substrate can be damaged by hightemperatures. Such "partial pyrolysis" or partial curing may be carriedout at temperatures lower than 500° C.

Depending on the preceramic polymer pyrolyzed, then, the ceramicproducts may include silicon nitride, silicon carbide, siliconoxynitride, silicon nitride/silicon carbide alloys, siliconnitride/boron nitride alloys, silicon carbide/boron nitride alloys, andmixtures thereof.

D. Ceramic Coating Procedures

The ceramic materials provided herein are useful in a number ofapplications, including as coatings for many different kinds ofsubstrates.

Silicon nitride and silicon oxynitride coatings may be provided on asubstrate, for example, by a variation of the pyrolysis method justdescribed. A substrate selected such that it will withstand the hightemperatures of pyrolysis (e.g., metal, glass, ceramic, fibers,graphite) is coated with a preceramic polymer material by dipping in aselected silazane or siloxazane polymer solution, or by painting,spraying, or the like, with such polymer solution, the solution having apredetermined concentration, preferably between about 0.1 and 100 wt. %,more preferably between about 5 and 10 wt. % for most applications. Thepolymer is then pyrolyzed on the substrate by heating according to thepyrolysis procedure outlined above. In such a method, pyrolysis can beconducted relatively slowly, i.e. at a heating rate between about 0.1°C. and 2.0° C. per minute, in order to allow evolved gas to escapewithout forming bubbles in the coating, and can include one or moreisothermal holding steps. In some instances, for example with relativelytemperature-sensitive materials, or where a rapid-coating process isdesired, a flash pyrolysis step may be preferred. Repeated, multiplecoatings may be applied where a thicker layer of material is desired,with partial curing or gradual or flash pyrolysis following eachindividual coating step.

The pyrolysis temperature will vary with the type of coating desired.Typically, temperatures will range from about 350° C. to about 1100° C.Lower temperatures, below about 500° C., can result in only partiallypyrolyzed polymer, as discussed in Section C.

Optionally, the liquid or dissolved polymer may be admixed with ceramicpowders such as silicon nitride or silicon carbide optionally admixedwith sintering aids such as aluminum oxide, silica, yttrium oxide, andthe like, prior to coating. Cross-linking agents as set forth in SectionC may be included in the coating mixture as well.

The above coating procedure is a substantial improvement over theconventional, chemical vapor deposition (CVD) method of producingsilicon nitride coatings in which the appropriate compounds (e.g., SiH₄and NH₃ or volatile silazane) react in the vapor phase to form theceramic which deposits on the target substrate. CVD is typically aninefficient, time-consuming process which requires costly andspecialized equipment. The procedure described above for producingcoatings containing silicon nitride can be done with a conventionalfurnace. Further, the method leads to heat-stable, wear-, erosion-,abrasion, and corrosion-resistant silicon nitride ceramic coatings.Because silicon nitride is an extremely hard, durable material, manyapplications of the coating process are possible. One specificapplication is in gas turbine engines, on parts which are particularlysusceptible to wear. Also, because silicon nitride is an insulator, thecoating process could be used as the dielectric material of capacitors,or for providing insulating coatings in the electronics industry. Otherapplications are clearly possible.

In an alternative embodiment of the invention, a substrate isspray-coated with ceramic or preceramic materials. Such a procedureprovides for a higher density coating, as well as for a greater degreeof homogeneity. Preceramic coatings may be provided on a substrate, orat higher temperatures, one or more ceramic coatings may be provided.Gaseous species, such as silane and ammonia, which are capable ofreacting to form preceramic polymers, are introduced into a nozzle. Thegases are admixed within the nozzle and passed over a transition metalcatalyst bed contained within the nozzle, suitable transition metalcatalysts herein are selected from those set forth in Tables I and II.The catalyst bed initiates the formation of preceramic materials fromthe gaseous species. At the nozzle, the gaseous preceramic materials aremixed with inert or reactive gases introduced into the apparatus throughone or more inlets, and the substrate surface is coated with a mixtureof these materials. Such a procedure, which provides a suspension ofliquid preceramic materials in air, may be used for the preparation offine powders, as well.

The desired polymerization reaction designated herein as type (a) ortype (b) thus takes place as the gases are passed over the catalyst bed.The inert gas delivers the preceramic materials to the substratesurface, or, if the gas phase is heated, it can deliver actual ceramicpowders or mixtures of powders and preceramic polymer havingcontrolled-size particles. The process can be used to form ultrafineaerosols of precursors and homogeneous catalyst solutions for ultrafineparticle applications.

E. Fabrication of Molded Ceramic Bodies

The preceramic polymers as provided herein, admixed with ceramicpowders, may be used to form three-dimensional articles by injection- orcompression-molding. In a preferred embodiment of the invention, apreceramic polymer/ceramic powder system is used to formthree-dimensional bodies by compression molding. The inventors hereinhave surprisingly discovered that there is chemical or physicalinteraction between the novel polysilazanes or polysiloxazanes and aceramic powder which includes Si₃ N₄ at temperatures as low as 800° C.Such chemical or physical reactions are not expected because evenultrafine-grained Si₃ N₄ powder containing sintering aids does notsinter at such low temperatures. After heating at 800° C. in N₂,cylindrical pellets containing both silicon nitride and polysilazaneshow volume shrinkage of up to 5% and considerable mechanical strength,while pellets of dry powder with no polymer added, heated under the sameconditions, show neither shrinkage nor enhanced mechanical strengthrelative to a powder compact pressed at room temperature. This aspect ofthe invention exploits the discovery of this chemical interaction toproduce ceramic bodies which can have, if desired, a very low porevolume. By using carefully selected conditions, three-dimensionalceramic forms can be prepared which have a green density of about 85%(or a pore volume of 0.06 cm³ /g or less). (If desired, however, lowerdensity materials can be made by the same process; see Examples 35-43.)

A polymer solution containing a polysilazane, e.g., [H₂ SiNCH₃ ]_(x),polysiloxane, or polysiloxazane is prepared and mixed with a ceramicpowder composition comprising, for example, silicon nitride, sinteringaids such as yttrium oxide; aluminum oxide; and silica and, optionally,fibers and whiskers of, for example, silicon nitride, silicon carbide,or carbon. The composition of the polymer/powder mixture is such that itcontains between about 5 and about 50 wt. % polymer, andcorrespondingly, between about 50 and about 95 wt. % ceramic powder. Themixture is loaded into a suitable form and compression molded at betweenabout 25,000 and about 50,000 psi. The formed body is then heated underan inert gas (or under ammonia or a gaseous amine compound) at atemperature between about 500° C. and about 900° C. to convert thepolymer to ceramic material. The body is then sintered at a temperatureof at least about 1600° C. at a pressure of at least about 3 atm N₂ orother gas in order to provide a very dense, substantially nonporousmaterial. The results as demonstrated in the examples indicate that theprocedure may also be successful in the absence of sintering agents.

F. Preparation of Fibers

The polymers provided in the present invention, and the substantiallylinear high molecular polysilazanes in particular, can be used forpreceramic fiber spinning.

Three general spinning techniques are commonly used: (a) melt spinning,in which the polymer is spun from its melt and solidified by cooling;(b) dry spinning, in which the polymer is at least partially dissolvedin solution and pulled out through the spinneret into a heat chamber,then solidified by solvent evaporation; and (c) wet spinning, in which aconcentrated polymer solution is spun into a coagulation or regenerationbath containing another solvent in which the polymer is not soluble.These methods are suitable for tractable high molecular polysilazaneshaving Mn≧10,000 D or Mw≧16,000D or Mz≧40,000D or combinations thereof,or containing a polymeric species in the resultant polymer distributionhaving a molecular weight over 50,000D. While these polymers may beeither meltable, malleable, or soluble in some types of solvents, theymay be insoluble in others (e.g., for wet spinning).

Additional relatively small quantities (0.1-5.0 wt. %) of a very highmolecular weight substantially linear organic polymer (100,000-5,000,000D) may be mixed with the inorganic polymer to support and improve thefiber strength after spinning, as taught in, e.g., U.S. Pat. Nos.3,853,567 to Verbeek and 3,892,583 to Winter et al.

The supporting technique is especially useful when low molecular weightand/or nonlinear polymers having a very low degree of chain entanglementare used.

One problem encountered in ceramic fiber fabrication derives from thefusability of inorganic polymers during pyrolysis. This fusabilityresults in structural problems in the spun fiber. Polymers produced bythe present invention, however, overcome the fusability problem,providing that the catalytic process as described herein is actuallyincorporated into the fiber-spinning process. For example, a highmolecular weight polysilazane may be mixed with homogeneous catalyst andheated in the spineret or in the curing chamber to cause reactions oftype (a) or (b) or both to occur and increase the degree ofcross-linking in the fiber. Alternatively, the spineret can itself be acatalytic bed. Cross-linking agents such as those set forth in Section Cmay also be included in the fiber-spinning process to provide additionalcross-linking; similarly, latent reactive groups (e.g., free aminomoieties) may be present, as well, for the same reason, even in theabsence of catalyst.

G. Other Applications

Many other applications of the novel polymers of the invention areclearly possible.

The results summarized in part G, for example, suggest combination ofpolysilazanes, polysiloxazanes, and related compounds with other ceramicpowders (e.g., SiC, BN, B₄ C) to produce composite articles. Such acomposite of, e.g., a siloxazane polymer/SiC powder mixture may give anarticle having improved oxidation resistance. Another application wouldbe to use the novel polymers in dissolved or liquid form as binderscombined with ceramic powders so as to provide a fluid polymer/powdermixture.

Infiltration and impregnation processes are

possibilities, as discussed, for example, in U.S. Pat. No. 4,177,230 toMazdiyasni et al. and in W. S. Coblenz et al. in Emergent ProcessMethods for High-Technology Ceramics, ed. Davis et al. (PlenumPublishing, 1984). Two general methods are typically used. One is ahigh-vacuum technique in which a porous ceramic body is contacted undervacuum with a liquid or dissolved preceramic polymer. After a highvacuum infiltration, the article is pyrolyzed to achieve a higherdensity. The second method is high-pressure infiltration. Either ofthese methods can be adapted for the polymers of the invention. Inaddition, low molecular weight oligosilazane solutions having highermobility in the porous ceramic body can be incubated with the ceramicbody and a transition metal catalyst, followed by curing of theoligomeric reactants to obtain reactions of type (a) or (b) or both. Insitu chain extension or cross-linking will reduce the mobility andvolatility of the oligomeric starting materials.

Other applications of the novel polymers include use as a cement to"bond" ceramic materials such as powders, ceramic fibers, andthree-dimensional forms. Bonding of fibers followed by pyrolysis canyield matrices or matrix composites. In some application, ceramicarticles may be joined by the polymers, under pressure, followed bypyrolysis. The chemical interactions discussed in part F between thepolymer and ceramic powders may occur in bonding to enhance the strengthof the cement.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, that theforegoing description as well as the examples which follow are intendedto illustrate and not limit the scope of the invention, which is definedby the scope of the appended claims. Other aspects, advantages andmodifications within the scope of the invention will be apparent tothose skilled in the art to which the invention pertains.

EXAMPLES

Experimental: Unless otherwise indicated, the reagents used wereobtained from the following sources: silanes, from Petrarch Systems,Inc., Bristol, Pa.; organic reagents including amines, from AldrichChemical Col, Milwaukee, Wis.; gases, from Matheson, Seacaucus, N.J.;and catalysts, from Strem, Newburyport, Mass.

EXAMPLE 1 Precursor Formation

Into a flame-dried three-neck flask equipped with an overhead mechanicalstirrer and an N₂ inlet was placed 500 ml anhydrous ether. This wascooled to <-70° C. in a dry ice/acetone bath. Dichlorosilane (150 g; 1.5moles) was then condensed into the flask. An excess of ≃198 g (4.5moles) monoethylamine was then added over a two-hour period. Thereaction mixture was stirred for an additional four hours, and the flaskwas then allowed to warm slowly overnight to room temperature. Thecontents were diluted with 500 ml ether and filtered to removemonoethylamine hydrochloride salt.

The solids were then placed in a 21 Erlenmeyer flask and stirred for 10minutes in 500 ml boiling THF. The mixture was filtered hot. Theextraction was repeated and the solids were rinsed with an additional500 ml hot THF. 89.0 g of products were obtained after solvent removal(81% yield) with Mn=490 D; Mw=1,720 D; Mz=11,370 D. Fractionation byhigh vacuum distillation (150°/300μ) gives 60% of volatile productshaving Mn of 307 D and 40% residue with Mn=420 D, Mw=2670 D, andMz=17,560 D.

EXAMPLE 2 Precursor Formation

Into a flame-dried three-neck flask equipped with an overhead mechanicalstirrer and an N₂ inlet was placed 500 ml anhydrous ether. This wascooled to <-70° C. in a dry ice/acetone bath. Dichlorosilane (150 g; 1.5moles) was then condensed into the flask. An excess of ≃300 mlmonomethylamine was then added over a two-hour period. The reactionmixture was stirred for an additional two hours. The flask was thenallowed to warm slowly overnight to room temperature. The contents werediluted with 500 ml ether and filtered to remove monomethylaminehydrochloride salt. The solvent fractions were evaporated under reducedpressure to yield 10-20 g (11-23%) of oil.

The low yield was attributed to poor extraction of the solids, as theweight of the solids was much higher than expected.

An improved method for the solid cake extraction was developed. Thereaction mixture was filtered and the solids rinsed with ether and THF.The solids were then placed in a 21 Erlenmeyer flask and stirred for 10minutes in 500 ml boiling THF. The mixture was filtered hot. Theextraction was repeated and the solids were rinsed with an additional500 ml hot THF. With this extraction method followed by solventevaporation the yield improved to 60-75%. The viscous oligomers obtainedafter evaporation of the solvent had normal average molecular weight(Mn) of Mn=800-1250 D. More than 85-95% of original product materialremained after high vacuum distillation (150° C./300μ) having Mn=1400 Dand higher. Soxhlet extraction can be used for the above cakeextraction.

EXAMPLE 3 Precursor Formation (Modified)

Into a flame-dried three-neck flask equipped with an overhead mechanicalstirrer and an N₂ inlet was placed 1 l anhydrous ether. This was cooledto <-70° C. in a dry ice/acetone bath. Dichlorosilane (154 g; 1.5 moles)was then condensed into the flask. Trichlorosilane, SHCl₃, 15.4 g (0.11mole), was added into the reactor. An excess of ≃400 ml monomethylaminewas then bubbled into the solution over a three hour period. Thereaction mixture was stirred for an additional two hours. The flask wasallowed to warm slowly overnight to room temperature. The contents werethen diluted with 500 ml ether and filtered to remove monomethylaminehydrochloride salt.

The solids were then placed in a 21 Erlenmeyer flask and stirred for 10minutes in 500 ml boiling THF. The mixture was filtered hot. Theextraction was repeated and the solids were rinsed with an additional500 ml hot THF. An excess of 20 ml monomethylamine was bubbled throughthe extracted solution at room temperature to complete removal ofchloride impurities. The cloudy solution was then filtered, followed byevaporation of solvent. The 89 g of oligomers obtained after evaporationof the solvent had Mn=1,780 D, Mw=7,460 D, and Mz=28,020 D. Nodistillation or purification was necessary.

EXAMPLE 4 Reaction of Diethylsilane with Ammonia

To 20.0 mmole of diethylsilane (1.76 g) were added 25 μmol of Ru₃ (CO)₁₂(16 mg). The solution was heated at 60° C. under approximately 80 psi ofNH₃. After 1 hour, 85% of the silane was converted to a mixture ofoligomers and the pressure increased by 200 psi due to H₂ evolution.Although Et₂ SiH₂ disappeared totally after 2 hours, chainoligomerization and cyclization continued for 12 hours. Oligomers oftypes A (n=3-5; major), B (n=1-4; major), C (n+n'=2 or 3), and D(n+n'+n"+n'"=2) were found in the product mixture. Small quantities ofother series--H[Et₂ SiNH]_(n) H (n=2-4) and H₂ N[Et₂ SiNH]_(n) H (n=2)also appeared in the solution. ##STR21## Thus, while some cyclomers wereproduced, most of the products were substantially linear oligomers.

EXAMPLE 5 Reaction of TMDS with Ammonia

To 30 mmole of tetramethyldisilazane (TMDS) were added 25 μmol of Ru₃(CO)₁₂. The solution was heated at 135° C. under 80 psi of NH₃. TMDSdisappeared totally after 20 h and polymerization continued for 28 h.The polymeric residue (heavy oil) was 2.44 gm (yield 61 wt %) afterdistillation at 180°/0.3 mm Hg, with an Mn of 764 D. The major polymericseries was the linear HSiMe₂ [NHSiMe₂ ]_(x) NHSiMe₂ H. Smaller, branchedchain polymers appeared as well. Molecular weights greater than 26000 Dcan be obtained by varying of reaction conditions.

EXAMPLE 6 Reaction of TMDS with Ammonia and Hydrazine

To 20 mmole of TMDS were added 25 μmol of Ru₃ (CO)₁₂. The solution washeated at 135° C. under 100 psi of NH₃. The conversion of TMDS was 94%after 1 h. 0.1 g of hydrazine were added and the solution was heatedagain for 3 hours. The GC results showed that most of volatile productsdisappeared. The high polymeric residue was 68 wt % after distillationat 180° C./0.3 mm Hg. Similar results are achieved by using 200 mg of 5%Pt/C (activated under H₂) using identical conditions. The number averagemolecular weight (Mn) is 1200 D.

EXAMPLE 7 Reaction of TMDS with Ammonia

To 75 mmole of TMDS were added 25 μmol of Ru₃ (CO)₁₂ and the solutionwas heated at 135° C. under 60 psi of ammonia. The hydrogen pressureproduced in the reaction was released every 1 hour and the reactor wascharged again with 60 psi of NH₃. TMDS disappeared after 5 h. Theinitial turnover frequency (TF) for TMDS disappearance was 260. The nettotal turnover number for Si--N bond production was close to 4,480 after8 hours.

EXAMPLE 8 Reaction of TMDS with Hydrazine

To 20 mmole of tetramethyldisilazane (TMDS) and 20 mmole anhydroushydrazine (NH₂ NH₂) were added 25 μmol of Ru₃ (CO)₁₂ and the solutionwas heated at 135° C. under nitrogen. All the TMDS disappears after 3hours and H₂ pressure was obtained (TF=528). The yield of the polymericresidue after distillation of the volatile products was 75 wt. %. Thenumber average molecular weight (Mn) was 968 D.

EXAMPLE 9 Reaction of n-Hexyl Silane with Ammonia

Ten (10.0) grams of n-hexyl silane and 16 mg of Ru₃ (CO)₁₂ as catalystwere heated at 60° C. under 150 psi of ammonia in a stainless steelreactor. A pressure of 300 psi was produced during the first hour. Thereactor was cooled to room temperature, the pressure was released andthe reactor was charged again with 150 psi of ammonia. This procedurewas repeated several times. After 1 hour, 68% of the substratedisappeared (according to calculations based on NMR analysis) and thereaction slowed down. After 17 hours, only 12% of the starting materialremained in the oily solution. Only a slight additional conversion wasdetected when the temperature was raised to 90° C. The addition ofanother 16 mg of Ru₃ (CO)₁₂ promoted further conversion to a viscousmaterial which appeared concurrently with the disappearance ofhexylsilane. The NMR and the VPO (vapor pressure osmometry) analyses areshown in Table 3.

                  TABLE 3    ______________________________________    Time  Form of      Conversion.sup.a                                  Unit's Ratio.sup.b    (hours)          Products     (%)        Si--H N--H  -- Mn    ______________________________________     1.sup.c          light oil    68         1.28  0.72  --    17.sup.c          slightly viscous                       88         1.18  2.18   921    24.sup.d          viscous oil  91         1.06  2.20   962    28.sup.d,e          very viscous oil                       100        0.70  1.84  2772    36.sup.d,e          wax          100        0.43  1.83  4053    ______________________________________     .sup.a Overall conversion was determined by NMR spectra in CDCl.sub.3     (ppm). For nhexylsilane: Si--H 3.52 (t, 3); C--H 1.36 (m, 8) and 0.92 (m,     5). For polysilazanes: Si--H 4.78 (m), 4.57 (m) and 4.36 (m); C--H 1.32     (m) and 0.91 (m); N--H 0.62 (m, br).     .sup.b Si--H and N--H unit ratios were determined by NMR using the hexyl     group integration as an internal standard.     .sup.c At 60° C.     .sup.d At 90° C.     .sup.e After addition of 16 mg Ru.sub.3 (CO).sub.12.

The reaction mixture was analyzed by NMR and GC-MS techniques todetermine types of polymer. In Table 5, possible polymer types A, B, C,D, and E are set forth with the elemental (C, H and N) analysis for eachin the upper part of the table. Actual analyses of the reaction mixtureafter 24 and 36 h are set forth in the lower part of the table.

Certain conclusions may be drawn from Table 4, as follows:

a. The initial conversion was very fast; the initial turnover frequencyfor silane conversion was 2350 per hour.

b. The polymer at 24 hours contained large quantities of Si--H bondseven when the molecular weights are high. Crosslinking was thereforeprevented, possibly as a result of steric hindrance.

c. At 36 hours the high integration ratio of N--H to C--H stronglysuggests that there are significant quantities of the ##STR22##functional groups. Si--NH₂ was also detected by I.R. (absorbance in 1550cm⁻¹ in CCl₄. [(NH)_(1/2) signifies that the NH group was shared withanother fragment of the polymer.]

d. The polymer product is believed to be a new composition of matter.

The GC-MS of the reaction solution showed a series of linear and cyclicoligomers with substituents on both the silicon, e.g., [(═N)₃ Si--)] andnitrogen, e.g., [(.tbd.Si)₃ N]. The terminal Si--NH₂ unit was notobserved in the GC-MS fragmentation patterns.

Referring to Table 4, the types of repeating units of A through E areset forth below. ##STR23##

                  TABLE 4    ______________________________________             Elemental Analysis    Type/hours % C          % H     % N    ______________________________________    A          55.81        11.63   10.85    B          52.94        10.66   15.44    C          50.00        11.11   19.44    D          59.25        11.93    5.76    E          58.37        11.35    7.57    28 h       54.51        10.95   10.84    36 h       52.54        10.73   12.93    ______________________________________

The following conclusions are drawn from Table 4. The actual analyses at28 h conform closely to the linear type A polymer.

This example illustrates additional reaction of type (a) or type (b)following an initial such reaction, (where, here, cross-linked polymersare prepared from initially synthesized linear oligomers. The polymerobtained by this method is believed to be a new composition of matter.

EXAMPLE 10 Reaction of Phenylsilane with Ammonia

Phenylsilane (10.0 g) and Ru₃ (CO)₁₂ (16 mg) were heated at 60° C. under150 psi of ammonia in a stainless steel reactor. The reactor was cooledseveral times during the reaction to sample and to recharge withammonia. After 3 hours, 84% of the phenylsilane was converted tooligomeric products (calculated from NMR data). After 14 hours, thereaction temperature was increased to 90° C., and after 18 hours 8 mgRu₃ (CO)₁₂ were added to the mixture. Table 5 summarizes theobservations and the results from the NMR and VPO analyses.

                  TABLE 5    ______________________________________    Time  Form of      Conversion.sup.a                                  Unit's Ratio.sup.b    (hours)          Products     (%)        Si--H N--H  -- Mn    ______________________________________     3.sup.c          slightly viscous                        84        1.21  0.98   549     9.sup.c          slightly viscous                        95        1.13  1.32  --    14.sup.c          very viscous  98        1.07  1.21   695    18.sup.d          hard wax     100        0.98  1.03  1058    28.sup.d,e          solid        100        0.47  1.47  --    32.sup.d,e          solid        100        0.34  1.70  1432    ______________________________________     .sup.a Overall conversion was determined by NMR spectra in CDCl.sub.3     .sup.b Si--H and N--H unit ratios were determined by NMR using the phenyl     group integration as an internal standard.     .sup.c At 60° C.     .sup.d At 90° C.     .sup.e Addition of 8 mg Ru.sub.3 (CO).sub.12 and 2 ml of toluene (removed     before molecular weight measurements).

The data for the 18 hour sample indicate the formation of linear Type Epolymers (see Table 6). As additional catalyst was added and thetemperature raised, more ammonia was incorporated into the polymer.After 32 h, the elemental and the NMR analyses indicate that the polymercontained units of types F, G, and H in the following approximateratios: ##STR24##

The polymer containing units F, G and H is indicated as I above.

This solid polymer I after 32 hours was soluble in CCl₄, CH₂ Cl₂, CHCl₃and toluene. It had a glass transition point at 70°-72° C. and softenedconsiderably at 90° C. Pyrolysis at 900° C. gave a 70% ceramic yield andfinally a 35% yield when heated to 1550°. Only alpha and beta Si₃ N₄were observed by X-ray powder diffractometry although the final ceramicproduct contained 29% carbon (as determined by elemental analysis). Theproduct is believed to be a new composition of matter.

                  TABLE 6    ______________________________________             Elemental Analysis    Type/hours % C          % H     % N    ______________________________________    F          59.50        5.78    11.57    G          56.25        5.47    16.40    H          52.94        5.88    20.58    18 h       59.37        5.67    11.81    32 h       57.42        5.58    14.21    I          57.25        5.60    14.97    ______________________________________

GC-MS analysis of the mixture after 3 hours of heating revealed thatmajority of the oligomers (n=1-3) were type F; minor products includedcyclic compounds, cyclomers with branching on a silane unit and straightand cyclic compounds branched on the nitrogen. Amine capped polymerswere not observed.

EXAMPLE 11 Reaction of a Hydridosilazane

HMeN[H₂ SiNM_(e) ]_(x) H (2.0 g; Mn=560) and Ru₃ (CO)₁₂ (16 mg) wereheated under several reaction conditions. The results are shown in Table7. The starting reactant --H₂ SiNMe]_(x) was prepared from H₂ SiCl₂ andMeNH₂ in ether solution as reported by Seyferth and Wiseman (PolymerChem. Div. Preprints; Paper presented at the spring meeting of ACS,April 1984). The products were [H₂ SiNMe]₄ and a linear oligomerHNMe[SiH₂ NMe]_(x) --H (x was approximately 10).

                                      TABLE 7    __________________________________________________________________________       Gas Phase             Temp.                 Time          Ceramic Yield (%).sup.a    Run       (atm) (°C.)                 (hours)                     Form of Product                               (Crystallized Form)    __________________________________________________________________________    1  H.sub.2 (1 atm)             60  4   viscous liquid                               68                     (Mn - 1180; soluble                     in toluene and                     CH.sub.2 Cl.sub.2)    2  H.sub.2 (1 atm)             135 2   soft rubber                               75    3  MeNH.sub.2             60  4   viscous liquid                               78       (3 atm)       (Mn = 1200)                               (αSi.sub.3 N.sub.4).sup.b    .sup. 4.sup.c       NH.sub.3             60  2   hard rubber                               85       (8 atm)                 (Si.sub.3 N.sub.4 : α > β)    __________________________________________________________________________     .sup.a Pyrolyzed under N.sub.2 by ramping the temperature to 900°     C. in 6 h and then holding for 2 h at 900° C.; sintered at     1550-1600° C.     .sup.b Poorly crystallized.     .sup.c Only 8 mg of Ru.sub.3 (CO).sub.12 were used.

EXAMPLE 12 Polymerization of Ethylsilane with Ammonia

Ethylsilane, (EtSiH₃, 8 g) was condensed into a stainless steel reactor,containing Ru₃ (CO)₁₂ (16 mg) in 1 ml of toluene, and cooled in a dryice/acetone container. The reactor was then pressurized with 100 psi ofammonia (at -78° C.). A total pressure of 250 psi was obtained when thereactor was heated (o room temperature. The solution was heated at 60°C. The reactor was cooled after 1 hour to room temperature,depressurized (releasing H₂), loaded with an additional 150 psi ofammonia and reheated at 60° C. for an hour, then cycled again for 2hours. The resulting solution (after 4 h) was very viscous. The solventwas evacuated (R.T., 0.1 mm) and the waxy polymer was heated again at90° C. for another 2 hours to form a soft rubber. Pyrolysis of therubber at between 200° and 900° C. gave 58% of ceramic material. The NMRand IR spectra of the polymer produced after 4 hours show the followingpeaks: NMR (8, CDCl₃) Si--H (4.90-4.40, m); CH₃ (0.95, t); N--H (1.0-0.8br); CH₂ (0.58, q). (The ratio of the Si--H to the Et--Si and N--Habsorbance was 1:24 which suggests that the polymer consists ofapproximately 30% [EtSiHNH] units and the rest were [Et(NH₂)SiNH and[Et(NH)₀.5 SiNH]). The product is believed to be a new composition ofmatter.

I.R. (cm⁻¹, CH₂ Cl₂), Si--NH--Si (3385, 1170, 950); Si--NH₂ (1545);Si--H (2108); Si--Et (1235, 1012).

EXAMPLE 13 Preparation of Polysiloxazane

1,1,3,3-Tetramethyldisiloxane (5.36 g, 40 mmole (HMe₂ Si)₂ O) and Ru₃(CO)₁₂ (32 mg, 50 μmol) were heated at 60° C. under NH₃ (150 psi). Thepressure produced in the reactor was released and the reactor wasrecharged with NH₃ several times. 80% of the disiloxane was convertedafter 1.5 hours. The reaction was heated continuously for 20 hours.

GC-MS analysis indicates the following pattern: ##STR25## A 70% yieldwas obtained after high vacuum distillation (180° C./0.5 mm).A.sub.(N=2) was isolated as solid white crystals, mp. 37° C., with asingle NMR absorption at 0.12 ppm. The residue was a viscous oil withMn=5690 D. (Mn values were measured by VPO techniques. Later resultsindicate that VPO may be insufficient for polymers having Mn over 2000.GPC results usually show higher values; see Example 14.)

    ______________________________________    Elemental analysis:                  % C     % H    % N   Si   O    ______________________________________    Polymer B     32.65   8.84   9.52  38.10                                            10.88    Found         32.67   9.10   8.56  41.89                                             7.02    ______________________________________

This is an example of preparing a polysiloxazane having the generalstructure: ##STR26## These polysiloxazanes are believed to be novelcompositions of matter. R' is as defined in the text. The nitrogen maybe substituted, e.g. by an organic group R, also defined earlier. Thesubscript n may have various values.

EXAMPLE 14 Reaction of Octamethylcyclotetrasilazane

Octamethylcyclotetrasilazane was reacted under various conditions with(+) and without (-) [(CH₃)₃ Si]₂ NH and with various catalysts. Resultsare set forth in Table 8. ##STR27##

                                      TABLE 8    __________________________________________________________________________    Yield of Oligomers and Polymers                               Yield (% Weight).sup.c    Run       Catalyst               [(CH.sub.3).sub.3 Si].sub.2 NH                       II Conv. (%).sup.b                               Oligomers                                     Polymers                                          M.W.    __________________________________________________________________________    1  H.sub.2 SO.sub.4               -       46      33    10   783    2  H.sub.2 SO.sub.4               +       46      18    33   587    3  Ru.sub.3 (CO).sub.12 /H.sub.2               -       74      54    18   2551    4  Ru.sub.3 (CO).sub.12 /H.sub.2               +       68      28    44   697    5  Pt/C    -       62      22    34   1080    6  Pt/C    +       71      28    45   784    __________________________________________________________________________     .sup.a The same conditions as shown in Table 9. The reactions were carrie     without internal standards and the analyses were made according to the     distillation of the solutions.     .sup.b The conversion measurement was due to the amount of cyclotetramer     in the end of the reaction.     .sup.c Yield was in weight percentage due to the total weight of the     solution. The oligomer fraction also contains the remains of disilazane     (Me.sub.3 Si).sub.2 NH.

GC-MS Analysis

Identification of polymer types produced in the reactions described inTable 8, were performed by GC-MS. This method was limited to polymerswith molecular weights less than 1000. We have observed types A and B inrun (1). B was the major product in run 4 (n=1-8) and A ##STR28##appears in small quantities (n=3-7). Another set of polymers observed ineven smaller quantities were C (n+n'=2-7) and D (n+n'+n"+n"'=2-6). C andD were crosslinked through nitrogen groups. ##STR29##

In the above, Si signifies --SiMe₂ -- and Si.tbd. signifies --SiMe₃.

In run 3, because of the high molecular weight, no significant productscould be detected by the GC-MS. Most likely there were more crosslinksfrom this run which also explains the high molecular weight. Run 6 showsthe same types as the parallel reaction with Ru₃ (CO)₁₂ but thequantities of C and D were larger. The Pt/C catalysis without thecapping agent gives series A and other quantitative series E F thatindicate bi- and tri-cyclo crosslinked compounds. ##STR30## F containsanother ring. In E, n_(total) (i.e. n+n'+n")=5-8; in F, n_(total) =8-9.

The polymers produced by H₂ SO₄ catalysis contains types A (n=5,6), B(n=2-8; major products), and C(n=2-5) in run 2 and A (n=5-9) in run 4.In both cases the GC-MS analyses show an amount of oxygenated productsin which oxygen replaced amine groups.

EXAMPLE 15 Reaction of polydimethylsilylhydrazine

To 1.8 g polydimethylsilylhydrazine H₂ NNH--[Me₂ SiNHNH]_(x) ]--Hprepared as follows:

    (CH.sub.3).sub.2 SiCl.sub.2 +NH.sub.2 NH.sub.2 →[(CH.sub.3).sub.2 SiNHNH].sub.n +NH.sub.2 NH.sub.3 Cl

(Mn˜1130) dissolved in 5 ml of toluene were added 25 μmol of Ru₃ (CO)₁₂and the solution was heated at 135° C. under hydrogen. The clearsolution turned cloudy and viscous (at room temperature). 1.3 g of asoft solid product was obtained after distillation of the volatileproducts and solvent at 180° C./0.3 mm Hg. The solid had an Mn of 1220 Dand started to soften at 60° C. The same treatment for the startingmaterial in the absence of catalyst gave a slightly cloudy solution atroom temperature (clear during heating). The Mn decreased to 612 D. Theproduct was a solid after distillation and did not soften up to 250° C.

This example illustrates the use of precursors having an N--N moietywithin the molecular structure.

EXAMPLE 16 Catalytic Studies

Octamethylcyclotetrasilazane was reacted with [(CH₃)₃ Si]₂ NH in thepresence of various catalysts. The reaction conditions, catalysts andresults are set forth in Table 9.

                                      TABLE 9    __________________________________________________________________________    n                                Decomposition    Run       Catalyst   Temp (°C.)                        Time (h)                             Conversion (%)                                     of Catalyst    __________________________________________________________________________     1 Ru.sub.3 (CO).sub.12                  135   6    22      s     2 Ru.sub.3 (CO).sub.12                  180   15   80      m     3 Ru.sub.3 (CO).sub.12 /H.sub.2                  135   1    78      --     4 Ru.sub.3 (CO).sub.12 /H.sub.2 O                  135   3    33      s     5 Ru.sub.3 (CO).sub.12 Fe(CO).sub.5                  135   6    26      s     6 Ru.sub.3 (CO).sub.12 Fe.sub.3 (CO).sub.12                  135   3    80      s     7 Fe.sub.3 (CO).sub.12                  135   3    80      s     8 Fe.sub.3 (CO).sub.12 H.sub.2                  135   3    80      f     9 Os.sub.3 (CO).sub.12                  135   --   --      --    10 Os.sub.3 (CO).sub.12                  180   20   78      --    11 Os.sub.3 (CO).sub.12 /H.sub.2                  135   6    73      --    12 H.sub.2 Os.sub.3 (CO).sub.10                  135   3    78      --    13 Rh.sub.6 (CO).sub.16                  135   20   55      g    14 Rh.sub.6 (CO).sub.16 /H.sub.2                  135   3    78      g    15 Ir.sub.4 (CO).sub.12                  135   --   --      --    16 Ir.sub.4 (CO).sub.12                  180   15   70      m    17 Ir.sub.4 (CO).sub.12 /H.sub.2                  135   3    76      f    18 Pt/C       135   3    75      --    19 PtO.sub.2  180   15   25      --    20 Pd/C       135   3    78      --    __________________________________________________________________________

Comments on Table 9 are as follows: The molar ratio ofoctamethylcyclotetrasilazane, silazane [(CH₃)₃ Si]₂ NH and catalyst was250:84:1. The reaction was carried out under hydrogen where indicated,as in Run No. 3, or with water in Run No. 4, otherwise under nitrogen.The hydrogen was at 1 atm. The time figures indicate the shortest timein which there was no further conversion of the starting silazanereactant. Butyl ether was used as an internal standard for gaschromatographic analysis. In the decomposition of catalyst column, "s"means slow, "m" means moderate and "f" means fast. In Run No. 4 theratio of Ru₃ (CO)₁₂ to H₂ O was 1:22. In Run No. 18, 200 mg of 5% Pt/Cwere used and in Run No. 20, 150 mg of 5% Pd/C were used with 4.15 gramsof octamethylcyclotetrasilazane.

EXAMPLE 17 Reaction of Hexamethylcyclotrisilazane with Ammonia andHydrogen

A reactor loaded with hexamethylcyclotrisilazane, (4.4 g) and Ru₃ (CO)₁₂(16 mg) was pressurized with NH₃ (150 psi) and H₂ (150 psi), then heatedat 135° C. for 18 hours. The cyclotrimer was converted in 84% yield toform two major series of products: cyclomers (A; n=4-13) and branchedcyclomers (B; n=1-6) analyzed by GC-MS. ##STR31##

EXAMPLE 18 Copolymerization of Phenylsilane and1,1,3,3-Tetramethyldisilazane

To a mixture of phenylsilane (4.32 g, 40 mmole) and1,1,3,3-tetramethyldisilazane (5.32 g, 40 mmole) was added Ru₃ (CO)₁₂(16 mg, 25 μmol). The solution was heated at 60° C. under 150 psi ofammonia. After 5 h, the GC shows high boiling products and the loss of95% of the starting materials. After 8 hours, the reaction temperaturewas increased to 90° C. and after another 2 hours to 135° C. Thereaction was run for 30 hours. The final result was a viscous oilconsisting of a mixture of products. Very little material came off theGC at this point which was indicative of high molecular weight products.Evaporation of the remaining volatile products (230° C./2 mm) leaves awaxy residue. IR, NMR and GC/MS of this product were taken to examinethe copolymerization between the two starting substrates. An Si--H bondappears clearly in the IR spectrum (although it is not observed in theNMR spectrum which was analytically less sensitive). The elementalanalysis and the NMR integration suggest that the copolymer contains thefollowing average structure.

    [Me.sub.2 SiNH].sub.2 ]Phenyl--SiHNH].sub.1.3

This copolymer is believed to be a new composition of matter.

    ______________________________________    Elemental analysis:                    C      H        N    Si    ______________________________________    Calculated for sug-                    46.69  7.61     15.23                                         30.44    gested structure:    Found           46.45  7.05     15.91                                         30.88    ______________________________________

EXAMPLE 19 Reaction Between Hexamethylcyclotrisilazane and Diethylsilane

15 mg (25 μmol) of Ru₃ (CO)₁₂ were added to 2.19 g (10 mmol) ofhexamethylcyclotrisilane (--Me₂ SiNH]₃) and 0.88 g (10 mmole) ofdiethylsilane (Et₂ SiH₂). The solution was heated at 135° C. for 20 h.

N-diethylsilane-hexamethylcyclotrisilazane ##STR32## was the majorproduct (3.7 mmole/ identified by GC-MS and NMR. Other minor productswere (HEt₂ Si)₂ NH and bis-(N-diethylsilyl)-hexamethylcyclotrisilazane.A residue of 28% yield remained after evaporation at 180° C. (0.5 mm).The (N-diethylsilyl)-cyclotrisilazane, believed to be a new compositionof matter, was isolated by distillation and identified by GC-MS and NMR.

EXAMPLE 20 Reaction of 1,2,3,4,5,6-Hexamethylcyclotrisilazane withAmmonia

To 4.39 g of [MeSiH--NMe]₃ were added 16 mg of Ru₃ (CO)₁₂. The solutionwas heated under 150 psi of ammonia at 60° C. The reactant disappearedafter 5 hours. The reactor was again charged with ammonia and heated at90° C. for 33 hours. The product was a viscous oil having Mn=691 whichgave a 57% yield of ceramic material. GC-MS analysis of the oligomericfraction indicated the substitution of Si--H groups by Si--NH groupstogether with the substitution of N--Me groups by N--H in the cyclomericstructure. The product is believed to be a new composition of matter.

EXAMPLE 21 Polymerization of Tetramethyldisilazane in the presence ofAmmonia

(a) To 100.0 mmole of TMDS (13.3 g) were added 50.0 μmol of Ru₃ (CO)₁₂(32 0 mg) and the solution was heated under ammonia under variousreaction conditions as noted in Table 10. The volatile oligomers wereseparated from the solution by vacuum distillation (up to 180° C./300μ).The residue was the nonvolatile fraction.

Our initial evaluation of this reaction, using either the homogeneousruthenium catalyst or activated Pt/C gave cyclomers (n=3-7), linearoligomers (n=2-11), and very small amounts of branched oligomers,(n=1-7; <5%) as evidenced by the GC-MS analyses.

                                      TABLE 10    __________________________________________________________________________    The Effects of Temperature and Ammonia Pressure on    Product Selectivity in the Reaction Between TMDS and NH.sub.3    in the Presence of Ru.sub.3 (CO).sub.12                   Turnover.sup.b                                 Yield of Cyclomers                   Frequency     in the Volatile                                            Nonvolatile    Temp.     Time.sup.a                   TMDS  Si--H   Fraction (%)                                            Oligomer                                                  Ave. M.W.    Run       NH (°C.)              (Hours)                   Conversion                         Disappearance                                 Total                                     Tricyclomer                                            Yield (%)                                                  (-- Mn)    __________________________________________________________________________    1   1 60  66    640  1000    39  25     19    1297    2   1 90  60    720  1160    34  18     21    1006    3  13 60  12   1220  1300    88  69     19    2024    4  13 90   8   1960  3438    91  70      5    1425    __________________________________________________________________________     .sup.a At these reaction time periods, the catalyst was still active but     the rate of reaction was considerably reduced because of the low Si--H     bond concentration.     .sup.b TF (mol substate/mol cat/h) based on initial rates, determined by     GC (TMDS conversion) and NMR integration (Si-- H signal disappearance)     referred to the CH.sub.3 --Si signals.

EXAMPLE 22 Catalytic Formation of Extended Polymers

An N-methylpolysilazane, CH₃ NH--(H₂ SiNCH₃ ]_(x) --H (Mn=1100) wasreacted with Ru₃ (CO)₁₂ under different conditions (e.g., reaction timeand temperature, ammonia and monomethylamine environment). Samples weretaken out of the reactions solutions; solvents were evaporated and Mnmeasurements were performed on VPO equipment. The results are shown inTable 11.

                                      TABLE 11    __________________________________________________________________________    Amounts       Polymer             Catalyst                  THF                     Gas  Tempera-                                Time                                   -- Mn (dal-    Run       (g)   (mg) (ml)                     Phase                          ture (°C.)                                (h)                                   tons)    __________________________________________________________________________    1  1.0    4.0 5.0                     N.sub.2                          60    10 1420    2  2.0    4.0 5.0                     N.sub.2                          60    20 1230    3  6.0   12.0 -- N.sub.2                          90    20 1620    4  6.0   24.0 12.0                     N.sub.2                          60    10 1550    5  6.0   24.0 12.0                     N.sub.2                          90    10 1380    6  6.0   12.0 12.0                     N.sub.2                          60    10 1300    7  4.0   16.0 8.0                     NH.sub.3                          60    10 Gel    8  4.0   16.0 8.0                     CH.sub.3 NH.sub.2                          60    10 Gel    __________________________________________________________________________

The polymers obtained in runs 7 and 8 were soluble in the reactionsolution and cross-linked upon solvent evaporation. Therefore, they areexcellent candidates for binder and coating applications. Runs 7 and 8prove the reactivity of the SiH polymers toward N--H bond additives andthe formation of increased amount of latent reactive groups providingthermosetting properties to the polymers.

EXAMPLE 23 Catalytic Formation of Extended Polymers

To 50 g N-methylsilazane CH₃ NH--(H₂ SiNCH₃)_(x) --H (Mn=1050) wereadded 100 mg Ru₃ (CO)₁₂ and the mixture was heated at 90° C. Sampleswere taken out of the solution and measured by GPC (Gel PermeationChromatography), VPO and Rheometry instruments. The results are shown inTable 12 and plotted in FIG. 1. All samples, including startingmaterial, show a very broad distribution. The higher molecular weightlimit (for observable species) was increased from 50,200 D in thestarting materials to 1,000,000 to 2,000,000 after 100 hours. Two newmaximum peaks are built up around 28,000 and 55,000 D. Althoughincreases in Mn were not observable after 40 hours, the higher molecularweight fraction continues to grow as indicated by the high Mw and Mzvalues, determined by GPC. These results are evidence of the extremelyhigh polymers which are obtained by the direct ammonolosis and by thecatalytic activation, chain extension and cross-linking. Such tractablehigh molecular weight products were never reported in the currentliterature. Separation of the high molecular weight fraction(s) may beeffected by either size exclusion chromatography, membrane orultrafiltration, ultracentrifugation, or solvent/solvent fractionationfrom solutions or high vacuum distillation. The polymer viscosityincreased dramatically during the reaction, starting at ˜1.0 poise andending at ˜400-4500 poise. All samples except the 100 hour one behave ina newtonian fashion. The 100 hour sample shows a non-Newtonian viscositybetween 4780 poise at a shear rate of 1.0 sec⁻¹ to 400 poise at a shearrate of 10.0 sec⁻¹.

                                      TABLE 12    __________________________________________________________________________    GPC.sup.a and Related VPO and Viscosity Results    Time        1st Max..sup.b             2nd Max..sup.b                   3rd Max..sup.b                         Highest                              -- Mn.sup.c                                  -- Mw.sup.c                                      -- Mz.sup.c                                           -- Mn.sup.d                                                  Viscosity    (hours)        (MW) (MW)  (MW)  (MW).sup.b                              (GPC)                                  (GPC)                                      (GPC)                                           (VPO)                                               D.sup.e                                                  (poise).sup.f,    __________________________________________________________________________                                                  i     0  2.1K --    --     50K 1,100                                   3,970                                      13,080                                           1050                                               3.6                                                   5    10  2.6K 23K   --    120K 2,040                                  10,450                                      38,220                                           1290                                               5.1                                                  --    20  2.6K 23K   50K   160K 2,130                                  12,660                                      47,010                                           1390                                               5.9                                                  --    30  2.6K 28K   50K   320K 2,140                                  17,990                                      86,840                                           1430                                               8.4                                                  18    40  2.6K 32K   55K   230K 2,280                                  19,510                                      78,430                                           1530                                               8.5                                                  55    50  2.6K 35K   55K   320K 2,570                                  20,990                                      86,710                                           1710                                               8.2                                                  58    65  2.6K 32K   60K   520K .sup. 2,320.sup.h                                  23,620                                      127,620                                           1760                                               10.6                                                  98    .sup. 100.sup.g        2.6K 33K   320K  2,480K                              .sup. 2,060.sup.h                                  46,290                                      553,020                                           --  23.0                                                  4,800    __________________________________________________________________________     .sup.a GPC equipped with 4 size exclusion columns suitable for separation     between 100 and 1,000,000 D. THF was used as a solvent and polystyrene     standardization curve.     .sup.b Maxima of the GPC distribution curve and highest molecular weight     species observed by GPC.     .sup.c Molecular weight determined by GPC.     .sup.d Measured by VPO techniques.     .sup.e D= dispersion of polymer; D = Mw/Mn.     .sup.f Measured by rheometer at 30° C.     .sup.g Difficulties were found in filtration; true values may be higher.     .sup.h Lower Mn may suggest branching or crosslinking of the polymer.     .sup.i The polymer behaves in a nonNewtonian fashion. For a sheer rate of     1.0 sec.sup.-1, the viscosity value was 4,800 poise. For a sheer rate of     10 sec.sup.-1, the viscosity value is 400 poise.

EXAMPLE 24 Reactions of Methylsiloxanes with Dimethylamine ##STR33##

To 6.0 g (100 mmole) ##STR34## were added 32 g (0.05 mmole) of Ru₃(CO)₁₂. The solution was charged with approximately 100 psi ofdimethylamine. The reaction was carried out at 60° C. and detected bythe observed pressure formed in the reactor. The pressure was releasedevery 0.5-1 hour and the reactor was recharged with fresh dimethylamine.After 6 hours, a total pressure of 1100 psi dimethylamine was chargedinto the reactor yielding a total pressure of 770 psi. No more gasevolution was observed. 8.1 g of viscous oily products were obtained,indicating 49% yield of amino substitution. This yield is correlatedwith the ¹ H--NMR analysis of the solution showing 53% of aminesubstitution and 29% of Si--H groups. GC-MS analysis shows that bis andtris substituted cyclotetramers were the major products when mono andtetrakis appear only in small quantities. The Mn of the product was 604D. Elemental analysis: Si(25.33); N(12.59); C(30.71); H(8.15); O(19.87).Pyrolysis under N₂ gave a ceramic yield of 14% and under NH₃ a ceramicyield of 61%.

b. [CH₃ SiHO]₂₉

The reaction was run with the same quantities of starting materials andunder the same conditions as the tetramer reaction of (a). Only 50 psiof dimethylamine was charged into the reactor each time. A totalpressure of 500 psi dimethylamine was charged and 375 psi of hydrogenwere evolved after 6 hours. 7.4 g of a very viscous polymer was obtained(33% yield of amino substitution) which was correlated to the ¹ H--NMRanalysis showing similar results (36% of amine substitution and 45% ofSi--H referred to the Si--CH₃ group). The Mn of the product was 1976.0D. Elemental Analysis: Si(28.89); N(7.77); C(28.68); H(7.51); O(20.85).Pyrolysis under N₂ and NH₃ gave ceramic yields of 25% and 70%,respectively.

EXAMPLE 25 Reaction of Silane with Ammonia

To a stainless steel reactor containing a solution of 32 mg Ru₃ (CO)₁₂in 10 ml THF were charged 40 psi of SiH₄ and 60 psi of NH₃. The reactorwas heated for 6 hours at 60° C. IR analysis indicates the formation ofsilazanes. A insoluble solid material (300 mg) obtained after solventremoval was characterized as intractable silazane resin. Elementalanalysis of this product shows THF or THF products trapped in the solidmaterial. This analysis fits the molecular structure of [(NH)₀.5SiHNH]_(x) after calculated corrections for the presence of THF productsand catalyst. Pyrolysis of the solid gave an 86% ceramic yield.

IR Analysis:

Solvent IR (THF), ref THF, cm⁻¹ :NH₂ 3380-3320; NH 3280; Si--H 2157,2142, 880; Si--NH₂ 11555; Si--NH--Si 1150, 972.

Solid IR (KBr, cm⁻¹): NH₂, NH 3700-3000; Si--H 2166, 885; Si--NH--Si1150, 1045, 960, (all very broad

    ______________________________________    Elemental Analysis of Polymer Product (%):    Si     N          H      C       O    Ru    ______________________________________    36.25  14.10      4.68   12.11   23.06                                          9.08    ______________________________________

Such a reaction may also be used in the preparation of ceramic products.

EXAMPLE 26 Reaction of Silane with Methylamine

To a stainless steel reactor containing a solution of 16 mg Ru₃ (CO)₁₂in 10 ml THF were charged 60 psi SiH₄ and 60 psi MeNH₂. The reactor washeated at 60° C. for 4 hours. A pressure of 120 psi was built up duringthe reaction period. The solution was homogeneous and 380 mg of oilyproducts remained after solvent removal. This oil became more viscous asa result of cross-linking at room temperature under inert atmosphere.Several ¹ H--NMR singlets of Si--H as well as 2 N--CH₃ singlets suggestdifferent types of silazane bonds. Indeed, GC-MS analysis providesevidence to the formation of cyclosilazanes containing aminic andsilylaminic side groups. ¹ H--NMR: Si--H 4.62, 4.49, 4.38 (7H); N--CH₃2.52, 2.48 (3OH).

EXAMPLE 27

Synthesis of Et₃ SiNH₂

To 20 mmole (3.2 ml) Et₃ SiH were added 0.05 mmole (11 mg) Pd(OAc)₂ andthe solution was heated at 100° C. under N₂ for 5 minutes to reducePd^(II) to Pd°. The solution was cooled to 21° C. and then dry ammoniawas bubbled through the solution to complete the silane transformationto silylamine in 4 hours. Completion of the reaction was observed by gaschromatography as well as by tapering off of the vigorous hydrogenevolution which occurred during the reaction. The reaction mixture wasfiltered under N₂ and distilled under N₂ (138° C.) to provideanalytically pure silylamine with yields higher than about 90%.

EXAMPLE 28 Reaction of Et₃ SiNH₂ with Et₃ SiH

To a solution of 9 mmole (2 ml) Et₃ SiNH₂ in 5 ml THF were added 16 mgof Ru₃ (CO)₁₂ and 9 mmole of Et₃ SiH. The reaction was completed after20 min at 70° C. and product formation (over 95% yield) was followed byGC.

EXAMPLE 29 Reactions of Oligo- and Polymethylsiloxane With Ammonia

a. 0.05 mmole (32 mg) Ru₃ (CO)₁₂ was added to 100 mmole (6.0 g)##STR35## and the solution was heated at 60° C. under 200 psi ofammonia. Gas evolution formed a pressure of 400 psi in 19 hours and hardrubber was formed. The product's elemental analysis showed the presenceof 5.55 Wt % which indicated a nitrogen-silicon ratio of 0.28 (Table13). Oxygen content was in a ratio of 1.29 per silicon. Some of theoxygen excess was a result of oxygen contamination found in thecommercial starting material and detected by NMR intensity ratio ofSi--H/Si--CH₃ absorbance (0.8:1.0). The product was pyrolyzed at 850° C.both under nitrogen and ammonia atmosphere. Elemental analysis of thepyrolyzed material suggested a mixture of the following ceramiccomponents (mol ratio): SiO₂ (0.62); Si₃ N₄ (0.23); SiC(0.14); C(0.58).Pyrolysis under a slow stream of ammonia reduced almost totally, thecarbon content as well a some of the oxygen excess and increasedsignificantly the nitrogen content.

Very similar results were observed when the cyclotetramer was replacedby polymethylsiloxane having a number average molecular weight (Mn) of1880 (degree of polymerization was 29) as shown in Tables 13 and 14. Thecomparison between cyclo and polysiloxane reactions revealed that lessnitrogen interacted with the polymer than with the cyclomer and the SiCfraction in the product pyrolyzed under nitrogen was higher for thepolymer reaction. However, no real difference was shown when both werepyrolyzed under ammonia. The pyrolysis was not completed as there was anexcess of oxygen (assuming that Si₂ ON₂ was the major product and thatthe silicon excess forms SiO₂). The ceramic yields were very high forall types of reactions and pyrolysis procedures.

b. A solution of 100 mmole (6.0 g) of ##STR36## and 25.0 μmol (8 mg) Ru₃(CO)₁₂ was heated at 60° C. under 100 psi of ammonia. After 2 hours 220psi of pressure were formed and the product was obtained as a viscousliquid having Mn=1230 D. The pressure was released and recharged with anadditional 100 psi of ammonia. 200 psi of gas were evolved in a 2-hourperiod and the viscous liquid was converted to a soft rubber.

¹ H NMR integration revealed that 41% of Si--H bonds were replaced byammonia to form Si--NH₂ and Si--NH-- bonds. Elemental analysis showedthat the incorporation ratio of 0.24 nitrogen per carbon, whichindicated the formation of cyclosilazane chain polymer bridged byammonia. A dimer of two cyclotetramers bridged by a single --NH was themajor product found by GC-MS analysis.

IR of CCl₄ solutions shows new sharp stretches at 3420 (w), 3380 (m)cm⁻¹ together with new shoulders at 1240 and 1160 cm⁻¹.

¹ H NMR (CDCl₃ δ, Ref CHCl₃): Si--H (4.69, 0.59H), NH (1.10, 0.16H) CH₃(0.22, 3H).

    ______________________________________    Elemental Analysis:                    C      H        N    Si    ______________________________________    Found (%)       19.94  6.14     5.39 42.23    mol ratio        1.00  3.70     0.24  0.91    ______________________________________

                  TABLE 13    ______________________________________    The Elemental Analysis of Polymers and Ceramics Ob-    tained in a Catalyzed Reaction Between Methylsiloxanes    and Ammonia              Analysis % (mole ratio)    Product     Si      O       N      C     H    ______________________________________    Cyclotetramer    Reaction    Polymer     40.70   29.85   5.55   18.02 5.88                (1.00)  (1.29)  (0.28) (1.03)                                             (4.06)    Ceramic material                45.73   32.53   6.94   14.10 0.79    under N.sub.2                (1.00)  (1.25)  (0.31) (0.72)                                             (0.48)    Ceramic material                47.76   28.26   21.81  1.35  0.57    under NH.sub.3                (1.00)  (1.04)  (0.91) (0.06)                                             (0.33)    Polymer Reaction    Polymer     42.47   27.80   4.06   19.67 6.00                (1.00)  (1.14)  (0.19) (1.07)                                             (3.95)    Ceramic material                48.12   32.81   5.02   13.65 0.76    under N.sub.2                (1.00)  (1.19)  (0.21) (0.66)                                             (0.44)    Ceramic material                48.29   28.35   21.01  1.75  0.54    under NH.sub.3                (1.00)  (1.03)  (0.87) (0.09)                                             (0.31)    ______________________________________

                  TABLE 14    ______________________________________    Ceramic Yield of the Pyrolyzed Polymers Ob-    tained in a Catalytic Reaction Between Methyl-    siloxanes and Ammonia    Reactant   Pyrolysis Conditions                             Ceramic Yield (%)    ______________________________________    Cyclotetramer               N.sub.2       77    Cyclotetramer               NH.sub.3      84    Polymer    N.sub.2       75    Polymer    NH.sub.3      88    ______________________________________

EXAMPLE 30 Kinetic Studies

In a typical kinetic reaction, a small quantity of the solid catalystwas carefully weighed and placed in a glass reactor. The reactor wasthen capped with a septum sealed head and the system was purged withargon for at least 15 minutes. Freshly dried THF, followed by 3.14 mmoleof triethylsilane, 0.513 mmole of n-decane and 2.38 mmole of n-butylamine were introduced into the reactor via syringe. The solution mixturewas then placed in an oil bath at 70° C. for reaction. Aliquots weredrawn out at timed intervals for GC analyses. In cases where reactiondid not occur at 70° C., the temperature was raised to 100° C.

                  TABLE 15    ______________________________________    Initial Reaction Rate of Catalytic    Reaction Between Et.sub.3 SiH and n-BuNH.sub.2                 Initial Reaction Rate    Catalyst     Relative to Ru.sub.3 (CO).sub.12    ______________________________________    Ir.sub.4 (CO).sub.12                 0.25.sup.a    Os.sub.3 (CO).sub.12                 0.30.sup.b    H.sub.2 Os.sub.3 (CO).sub.10                 0.45.sup.b    Rh.sub.6 (CO).sub.16                 0.17.sup.a    Ru.sub.3 (CO).sub.12                 1.00.sup.a    H.sub.4 Ru.sub.4 (CO).sub.12                 0.03.sup.a    PdCl.sub.2   13.3.sup.a    Pd/C         5.62.sup.a    Pd(OAc).sub.2                 12.8.sup.a    (φCN).sub.2 PdCl.sub.2                 16.9.sup.a    Pt/C         0.18.sup.a    ______________________________________     .sup.a Bath temperature 70° C.     .sup.b Bath temperature 100° C.

EXAMPLE 31 Gradual Pyrolysis of Silazanes

For polysilazane polymers based on n-methyl polysilazane, CH₃ NH--(H₂SiNCH₃)_(x) --H with average x>10, that were reacted with Ru₃ (CO)₁₂catalyst and other components, e.g., MeHN₂, Me₂ NH, and NH₃, we havedetermined that the yield for conversion to ceramic material when heatedin N₂ atmospheres were strongly dependent on heating rate. Polymersheated in N₂ at 0.5° C./min gave yields between 67-70 wt % (ceramicmaterial) while polymers heated at 5° C./min gave yields of under 60%.The maximum temperature for these pyrolyses reactions was ˜800° C. Ithas also been found that isothermal holds during pyrolysis at ˜110° C.for 3 hours additionally increased the ceramic yields by up to 6 wt %.Yield differentials with respect to heating rate variations can becorrelated with differences in weight loss versus temperature between300°-500° C. While not wishing to be bound by any particular theory, itis postulated that yield differentials with respect to the presence orabsence of isothermal curing steps during pyrolysis may be due to latentreactivity of Si--H bonds and the presence of small amounts of catalystin the polymer.

EXAMPLE 32 TGA Pyrolysis

To 10 g of CH₃ NH--(H₂ SiNCH₃)_(x) --H prepared as in Example 2 wereadded 20 mg of Ru₃ (CO)₁₂ and the solution was heated at 90° C. for 8 h.The viscous polymer obtained in the reaction was then pyrolyzed in TGAequipment at temperature ramping rates of 5.0° C./min and 0.5° C. perminute. FIG. 2 shows the dependence of the ceramic yield on the heatingrate. The weight lost between 200° C. and 400° C. was retarded by about10% in the slow pyrolysis due to the increase in thermal cross-linkingreactions and the decrease in volatilization of compounds. At thistemperature range, the products evaporated out of the resin materialwere mostly low molecular weight silazane oligomers. Below 200° C., theweight lost was primarily due to hydrogen and methylamine release,suggesting that control of the temperature within this range increasesthe amount of cross-linking in the pyrolyzed material.

EXAMPLE 32 Pyrolysis Under N₂ or NH₃

Various polymers containing [H₂ SiNCH₃ ] monomeric units were pyrolyzedunder N₂ and ammonia at different temperature ramping rates (see Table16). Table 16 indicates the following: (1) slow pyrolysis rates increasethe ceramic yields; (2) low temperature holds during the pyrolysisschedule slightly increase the ceramic yields; (3) higher molecularweights give in general higher ceramic yields; (4) extended polymersproduced by catalytic activity give higher ceramic yields; and (5)polymers treated with catalyst in the presence of ammonia give higherceramic yields than in the absence of ammonia.

Table 17 shows the elemental analysis of pyrolyzed polymers fromdifferent runs set forth in Table 16. As may be seen in Table 17, thecarbon content of ceramics derived from polymer reacted with catalyst inan ammonia or gaseous amine atmosphere was significantly lower thanpolymer reacted under nitrogen. Pyrolysis under ammonia or other aminethus substantially reduces the carbon content of the ceramic product.

                                      TABLE 16    __________________________________________________________________________    Pyrolysis of [H.sub.2 S:NCH.sub.3 ].sub.x -based Polymers    Polymer Type      Reaction Conditions   Pyrolysis Conditions       Mn; synthesis; polymer:                      Temp                          Time                              Gas Phase     Heating                                                 Gas  Holds                                                           Ceramic Yield    Run       catalyst wt ratio:                      (°C.)                          (hours)                              (psi) Product Phase                                            °C./min                                                 phase                                                      (°C;                                                           (900°    __________________________________________________________________________                                                           C.)    1  .sup.a Mn = 323; direct ami-                      --  --  --    nonvisc liq                                            5.0  N.sub.2                                                      --   28       nolosis at 0° C.    2  .sup.a Mn = 566; nonvolatile                      --  --  --    nonvisc liq                                            5.0  N.sub.2                                                      --   38       fraction of 1.    3  Mn = 800; direct aminol-                      --  --  --    visc liq                                            0.5  N.sub.2                                                      --   45       osis at -78° C.; with-       out volatiles distil-       lation.    4  Mn = 1100; as in 3.                      --  --  --    visc liq                                            0.5  N.sub.2                                                      --   49    5  Mn = 1770; as in 3 with                      --  --  --    visc liq                                            0.5  N.sub.2                                                      --   45       10% HS:Cl.sub.3    6  Mn = 1490; with Ru.sub.3 (CO).sub.12 :                      90   8  N.sub.2                                    visc liq                                            5.0  N.sub.2                                                      --   54       500; starting Mn = 1150    7  As in 6        90   8  N.sub.2                                    visc liq                                            0.5  N.sub.2                                                      --   64    8  As in 6        90   8  N.sub.2                                    visc liq                                            0.5  N.sub.2                                                      130:24                                                           66    9  As in 6        90   8  N.sub.2                                    visc liq                                            0.5  N.sub.2                                                      200:24                                                           68    10 Mn = 1600; as in 9                      90  20  N.sub.2                                    vy visc liq                                            0.5  N.sub.2   67    11 .sup.b Mn > 1800; as in 10                      90  26  CH.sub.3 HN.sub.2                                    visc liq (wax)                                            0.5  N.sub.2   69    12 As in 11       90  26  CH.sub.3 NH.sub.2                                    visc liq (wax)                                            5.0  N.sub.2   57    13 .sup.c gel; with Ru.sub.9 (CO).sub.12 :                      60  10  NH.sub.3                                    soft rubber                                            0.5  N.sub.2                                                      --   77       in THF; 250    14 As in 13       60  20  NH.sub.3                                    soft rubber                                            0.5  N.sub.2                                                      --   83    15 As in 4        --  --  --    visc liq                                            0.5  NH.sub.3                                                      --   49    16 As in 6        90   8  N.sub.2                                    visc liq                                            0.5  NH.sub.3                                                      --   65    __________________________________________________________________________     .sup.a Reported by Seyferth et al.     .sup.b Partially insoluble in toluene for VPO measurements.     .sup.c Saluble in THF solution, crosslinked during solvent removal.

                  TABLE 17    ______________________________________    Elemental Analysis                 Elemental Analysis    Run          (mole ratio)    (From Table 16)                 Si       N      C      H    O    ______________________________________     4           45.8     32.5   18.8   1.0  2.0     6           48.8     32.8   17.5   0.8  0.1    12           45.0     34.0   18.9   0.8  1.4    13           49.3     31.5   16.2    1.10                                             2.2    15           52.0     34.0    0.7   1.2   1.55    16           56.0     32.6    4.3   0.7  0.1    ______________________________________

EXAMPLE 34 Silicon Oxynitride Ceramic

X-ray powder diffraction analyses of the ceramic products obtained bythe procedure described in Example 29 show a clear spectral pattern oforthorhombic Si₂ ON₂ when the polymeric products were pyrolyzed underNH₃ (pyrolysis under N₂ gave relatively poor crystallization under thesame conditions). These patterns are found only when the total amorphousceramic products produced at 900° C. are reheated to 1600° C. under N₂.No other types of ceramic crystallites were observed in the X-ray powderdiffraction spectra. Less than 0.45 wt. % carbon was found, and thesilicon content of the product was 51-56 wt. % (theoretical: 56 wt. %),suggesting substantially pure silicon oxynitride in the ceramic mixture.

EXAMPLE 35 Fabrication of Ceramic Articles Using Silicon Nitride as aBinder

This example illustrates a process for the fabrication of ceramic bodiesfrom a mixture of preceramic polysilazane and ceramic powders. Thesilicon and nitrogen containing polymers as prepared in the previousExamples display controllable chemical, mechanical, rheological, andpyrolytic properties that make them suitable as binders or forming aids.When mixed with ceramic powders such as Si₃ N₄, the polymer/powdersystem can be compression molded into a variety of shapes. Pyrolyticrelease of the organic components bound to the polysilazane above 800°C. provided an amorphous Si₃ N₄ material that partially fills the poresystem that exists in powder compacts. This partial filling decreasesthe porosity of the body and increases its green density, which isadvantageous for subsequent sintering steps at temperatures in excess of1700° C.

The preceramic polymer used in this process was a polysilazane havingthe approximate structure (H₂ SiNCH₃)_(x). This polysilazane wassynthesized by the procedure described in U.S. Pat. No. 4,612,383, citedsupra. This method allows for control of the degree of polymerizationand the viscosity of the polysilazane, an important characteristic forany binder material. In a typical experiment, (H₂ SiNCH₃)_(x) (M_(n)=1265 D; viscosity˜1 poise) was heated at 90° C. for 55 h with Ru₃(CO)₁₂ as catalyst. It was then dissolved in THF and filtered. Thesolvent was removed by vacuum evaporation (P_(Hg) ˜1 mm). The resultingpolymer (M_(n) =1420 D; viscosity˜50 poise; density=1.03 g/cm³) wasredissolved in THF to form a standard solution of 0.059 g/ml. A powdersuch as Si₃ N₄ was added to the standard solution in different mixingratios and dispersed ultrasonically. THF was again removed by vacuumevacuation, leaving a homogeneous polymer/powder mixture. The mixturewas loaded into a steel die and under an inert atmosphere of N₂ andcompression molded at pressures of 5000 to 45,000 psi. The die wascoated with tetramethyldisilazane or hexamethyldisilazane as a moldrelease. The formed body, already a rigid article hard enough to bedisplaced without any significant precautionary measures (other thanreduction of exposure to moisture), was then heated to ˜800° C. in N₂ at0.5°-5° C./min to convert the polymer to ceramic material. The pyrolyzedbodies have densities up to 2.9 g/cc, indicating porosities of less than15% for unsintered pieces. Sintering of the body to final density occursat 1725° C. in an overpressure of N₂.

By contrast, polymer/powder mixtures were also processed by mechanicalmixing of liquid polysilazanes with ceramic powder. This variation ofthe above procedure resulted in inferior formed bodies caused byinsufficient homogeneity of the polymer/powder mixture due to inadequatemixing. The consequence of this was an unsatisfactory distribution ofpolymer with respect to the ceramic powder. The sintered bodiesfabricated by this method had final densities of 2.7 g/cc or less. Thisdemonstrates the efficacy of solution mixing of polymer and powder toachieve homogeneity. Using a stock solution of polymer also simplifieshandling of these oxygen- and water-sensitive polymers.

A range of polymer/powder ratios have been examined from 10-30 wt %polymer. Polymer/powder ratio can have a crucial effect on the greendensity of the pyrolyzed body and the degree of damage during pyrolysis.The optimum ratio of 15-20 wt % polymer ensures the maximum greendensity with enough porosity in the pressed body to ensure that volatilecomponents of the polymer can be removed during pyrolysis without damageto the body.

EXAMPLE 36

Preparation of Ceramic Bodies from Preceramic polysilazane and CeramicPowders

A polysilazane CH₃ NH--(H₂ SiNCH₃)_(x) --H as prepared in Example 2(M_(n) =1100 D; viscosity˜1 poise) was heated at 90° C. for 55 h withRu₃ (CO)₁₂ as catalyst. It was then dissolved in THF and filtered. Thesolvent was removed by vacuum evaporation (P_(Hg) ˜1 mm). The resultingpolymer (M_(n) =1420 D; viscosity˜50 poise; density=1.03 g/cm³) wasredissolved in THF to form a standard solution of 0.059 g/ml. A ceramicpowder consisting of 79.81 wt. % Si₃ N₄, 11.37 wt. % Y₂ O₃, 5.69 wt. %Al₂ O₃, and 3.13 wt. % SiO₂ was mixed in a ball mill for 24 h with Si₃N₄ balls and methanol. After evaporation of the methanol, 8.002 g ofpowder were added to 33.90 ml of polymer solution and dispersedultrasonically. The THF was removed by vacuum evacuation, leaving ahomogeneous powder/polymer that was 80 wt. % ceramic powder and 20 wt. %polymer. The mixture was loaded in a steel die under N₂ and compressionmolded at 27,000 psi. The die was coated with tetramethyldisilazane as amold release. The formed body was heated under 1 atm N₂ at 0.5° C./minto 800° C. to convert the polymer to ceramic material. The volume ofpores in this pre-sintered piece was 0.114 cm³ /g. which corresponds toa green density of 75%. The piece was then sintered at 1725° C. at 8 atmof N₂ for 6 h. After sintering, the piece was over 95% of theoreticaldensity with no open porosity.

EXAMPLE 37 Preparation of Ceramic Bodies

A polysilazane solution and a ceramic powder composition were preparedas in the previous Example. The ceramic powders were mixed with Si₃ N₄and methanol as in the previous Example, and the methanol wasevaporated. 10.20 g of powder were added to 30.40 ml of polymer solutionand dispersed ultrasonically. The THF was removed by vacuum evacuation,leaving a homogeneous powder/polymer that was 85 wt. % ceramic powderand 15 wt. % polymer. The mixture was loaded in a steel die under N₂ andcompression molded at 27,000 psi. The die was coated withhexamethyldisilazane as a mold release. The formed body was heated under1 atm N₂ at 0.5° C./min to 800° C. to convert the polymer to ceramicmaterial. The volume of pores in this pre-sintered piece was 0.15 cm³/g, which corresponds to a green density of 68%. The piece was thensintered at 1725° C. at 8 atm of N₂ for 6 h. As in the previous Example,after sintering, the piece was over 95% of theoretical density with noopen porosity.

EXAMPLE 38 Preparation of Ceramic Bodies

A polysilazane solution and a ceramic powder composition were preparedas in Example 35. The ceramic powders were mixed with Si₃ N₄ andmethanol as in Example 35, and the methanol was evaporated. 7.51 g ofpowder were added to 42.40 ml of polymer solution and dispersedultrasonically. The THF was removed by vacuum evacuation, leaving ahomogeneous powder/polymer that was 75 wt. % ceramic powder and 25 wt. %polymer. The mixture was loaded in a steel die under N₂ and compressionmolded at 45,000 psi. The die was coated with hexamethyldisilazane as amold release. The formed body was heated under 1 atm N₂ at 0.5° C./minto 800° C. to convert the polymer to ceramic material. The volume ofpores in this pre-sintered piece was 0.09 cm³ /g, which corresponds to agreen density of 79%. The bodies showed damage after molding andpyrolysis due to excess polymer in the mixture which prevented anoptimal powder/polymer ratio from being achieved. The volume fraction ofthe powder fell below 50%, indicating that the powder particles were notin contact in the molded body.

EXAMPLE 39 Preparation of Ceramic Bodies

A polysilazane solution and a ceramic powder composition were preparedas in Example 35. The ceramic powders were mixed with Si₃ N₄ andmethanol as in Example 35, and the methanol was evaporated. 7.51 g ofpowder were added to 42.40 ml of polymer solution and dispersedultrasonically. The THF was removed by vacuum evacuation, leaving ahomogeneous powder/polymer that was 75 wt. % ceramic powder and 25 wt. %polymer. The mixture was loaded in a steel die under N₂ and compressionmolded at 27,000 psi. The die was coated with tetramethyldisilazane as amold release. The formed body was heated under 1 atm N₂ at 0.5° C./minto 800° C. to convert the polymer to ceramic material. The volume ofpores in this pre-sintered piece was 0.06 cm³ /g, which corresponds to agreen density of 85%. The bodies showed damage after molding andpyrolysis due to excess polymer in the mixture which prevented anoptimal powder/polymer ratio from being achieved. The volume fraction ofthe powder fell below 50%, indicating that the powder particles were notin contact in the molded body.

EXAMPLE 40 Preparation of Ceramic Bodies

A polysilazane solution and a ceramic powder composition were preparedas in Example 35. The ceramic powders were mixed with Si₃ N₄ andmethanol as in Example 35, and the methanol was evaporated. 9.00 g ofpowder were added to 17.00 ml of polymer solution and dispersedultrasonically. The THF was removed by vacuum evacuation, leaving ahomogeneous powder/polymer that was 90 wt. % ceramic powder and 10 wt. %polymer. The mixture was loaded in a steel die under N₂ and compressionmolded at 27,000 psi. The die was coated with tetramethyldisilazane as amold release. The formed body was heated under 1 atm N₂ at 0.5° C./minto 800° C. to convert the polymer to ceramic material. The volume ofpores in this pre-sintered piece was 0.25 cm³ /g, which corresponds to agreen density of 56%. The piece is then sintered at 1725° C. at 8 atm ofN₂ for 6 h. As in the foregoing Examples, after sintering, the piece isover 95% of theoretical density with no open porosity.

EXAMPLE 41 Preparation of Ceramic Bodies

A polysilazane solution was prepared as in Example 35. To 30.4 ml ofthis solution were added 10.20 g of pure silicon nitride powder, and thesuspension was dispersed ultrasonically. The THF was removed by vacuumevacuation, leaving a homogeneous powder/polymer that was 85 wt. %ceramic powder and 15 wt. % polymer. The mixture was loaded in a steeldie under N₂ and compression molded at 27,000 psi. The die was coatedwith hexamethyldisilazane as a mold release. The formed body was heatedunder 1 atm N₂ at 0.5° C./min to 800° C. to convert the polymer toceramic material. The volume of pores in this pre-sintered piece was0.106 cm³ /g, which corresponds to a green density of 77% Inspection ofthe microstructure of the piece with SEM analyses showed chemical orphysical reaction between the polymer-derived material and the siliconnitride powder (see FIG. 3). This indicated the capability of using thissystem for solid state sintering of Si₃ N₄ powder. Upon treatment to1725° C. at 8 atm N₂, considerable grain growth occurred, although poreclosure was not achieved (see FIG. 4). This is further evidence of solidstate reactions occurring in a silicon nitride powder/polymer-derivedglass system.

EXAMPLE 42 Preparation of Ceramic Bodies

A polymer solution was prepared as in Example 35, and mechanically mixedwith a ceramic powder consisting of 79.81 wt. % Si₃ N₄, 11.37 wt. % Y₂O₃, 5.69 wt. % Al₂ O₃, and 3.13 wt. % SiO₂. The mixture contained 2.04 gof ceramic powder and 0.83 g of polymer for a mixture that was 71 wt. %powder and 29 wt. % polymer. The mixture was compression molded in asteel die at 15,000 psi using a hexamethyldisilazane mold release, andheated in vacuum at 150° C. while in the mold. The molded body wasinferior in quality to that of the previous Examples because ofinsufficient homogeneity of the powder/polymer mixture, in turn due toinadequate mixing. The body was heated to 500° C. in N₂ at 2° C./min,held at 500° C. for 3 h, and then heated to 900° C. at 1° C./min. Crackswere seen in the body before and after pyrolysis. Upon sintering at1725° C. for 6 h in 8 atm N₂, the body achieved only 80% of theoreticaldensity.

EXAMPLE 43 Preparation of Ceramic Bodies

A polysilazane solution (CH₃ NH[H₂ SiNCH₃ --_(x) H, Mn˜1100 D) wasprepared substantially as in the previous Examples; in this Example,however, the polysilazane was not previously treated with catalyst.8.502 g of ceramic powders (as set forth in Example 35) were mixed with1.5 g polymer in a THF solution. The mixture was compression-molded in asteel die at 15,000 psi and pyrolyzed under N₂ as in the precedingExample. Upon the heating schedule described in the previous examples, agreen density of about 72% was found.

EXAMPLE 44 Polysilazane Coatings

Coatings of polysilazane precursors were prepared by dipping flat,polished, stainless steel plates (11/4×11/4×1/16 inch) into polysilazanesolutions (type CH₃ NH--(H₂ SiNCH₃)_(x) --H, Mn˜1400) in THF havingconcentrations of 5 wt. %, 10 wt. % and 20 wt. %. The samples were curedunder the slow pyrolysis regime (heating rate of 100° C./hr) to a finaltemperature of 700° C. The cured coatings were shiny, transparent andsmooth. Coatings on the stainless steel plates were brightly coloredfrom the interference of reflected light. The thickness of the curedcoating was estimated from the interference colors to be between 0.1 and0.5 microns for the two dilute solutions and between 0.5 and 1.5 micronsfor the 20% solution. Light micrographs of the thin and the thickcoatings showed that while thin coatings appeared quite uniform, thickercoatings displayed cracks and irregularities due to shrinkage duringpyrolysis.

EXAMPLE 45 Polysilazane Coatings

To obtain thicker ceramic coatings, triple layered coatings ofpolysilazane precursors were prepared by dipping flat stainless steelplates (as in Example 44) in polysilazane/THF solutions having weightconcentrations of 5% and 10%. The polysilazane used was the same as thatin Example 44. Pyrolysis was conducted between each coating stepaccording to a gradual pyrolysis regime (100° C./min temperatureramping) to a final temperature of 700° C. The coatings so prepared hada thickness of about 0.1-2.0μ and appeared substantially smooth anduniform.

EXAMPLE 46 Fiber Preparation

A polymer of type CH₃ NH--(H₂ SiNCH₃)_(x) --H was extended by catalytictreatment with Ru₃ (CO)₁₂ substantially as discussed in Example 23. Theextended polymer had an Mn of 2100 D and viscosity of 90 poise. Thepolymer (4.0 g) was mixed with 1.0 wt. % of monodispersed polystyrene(0.4 g) having an Mn=1,800,000 D in 20 ml THF. The solvent was removedby evaporation after both polymers were completely dissolved in thesolution. The very viscous liquid was transferred into a narrow-mouthglass container and placed under argon in a sealed glass cylinderequipped with a stainless steel wire, inlet and outlet for gases, and aheating element and thermocouple. The argon atmosphere was replaced byammonia and fibers of 4 to 8" were pulled out of the viscous polymermixture by the wire. These fibers maintained their shape after a curingperiod of 0.5 h under ammonia without any flaws or breakage.

We claim:
 1. A method of producing polysilazanes useful as preceramicpolymers and containing at least one newly formed Si--N bond whichcomprises:(a) providing a precursor containing at least one Si--N bond,catalytically cleaving an Si--N bond in the precursor in the presence ofa transition metal catalyst effective to activate Si--N bonds, suchcleavage being carried out in the presence of hydrogen or a hydrogendonor, and reacting the cleavage product to produce an initialpolysilazane product; or (b) providing one or more reactants whichcontain an Si--H bond and an N--H bond, and causing reaction to occurbetween such Si--H and N--H bonds in the presence of a transition metalcatalyst effective to activate Si--H and N--H bonds, to produce aninitial polysilazane product having at least two Si--N bonds.
 2. Themethod of claim 1, wherein in said type (a) reaction, said initialpolysilazane product results from reaction of said cleavage product isreacted with a second such cleavage product or with a compoundcontaining an Si--H bond, an N--H bond, or both.
 3. The method of claim1, wherein a compound having an M--H bond reacts with either thecleavage product in said type (a) reaction or with a reactant in saidtype (b) reaction or both, wherein M is B, Al, Ga, In, Ge, Pb, Sn or S.4. The method of claim 1, wherein the transition metal catalyst is ahomogeneous catalyst selected from the group consisting of H₄ Ru₄(CO)₁₂, Fe(CO)₅, Rh₆ (CO)₁₆, Co₂ (CO)₈, (Ph₃ P)₂ Rh(CO)H, H₂ PtCl₆,nickel cyclooctadiene, Os₃ (CO)₁₂, Ir₄ (CO)₁₂, (Ph₃ P)₂ Ir(CO)H, NiCl₂,Ni(OAc)₂, Cp₂ TiCl₂, (Ph₃ P)₃ RhCl, H₂ Os₃ (CO)₁₀, Pd(Ph₃ P)₄, Fe₃(CO)₁₂, Ru₃ (CO)₁₂, ZnCl₂, RuCl₃, NaHRu₃ (CO)₁₁, PdCl₂, Pd(OAc)₂, (φCH)₂PdCl₂, and mixtures thereof, or a heterogeneous catalyst selected fromthe group consisting of Pt/C, Pt/BaSO₄, Cr, Pd/C, Co/C, Pt black, Coblack, Ru black, Ra--Ni, Pd black, Ir/Al₂ O₃, Pt/SiO₂, Ru/TiO₂, Rh/La₂O₃, Pd/Ag alloy, LaNi₅, PtO₂, and mixtures thereof.
 5. The method ofclaim 1, wherein said transition metal catalyst is a palladium catalyst.6. The method of claim 1, wherein the reaction temperature is betweenabout -78° C. and about 250° C.
 7. The method of claim 1, wherein thepolysilazanes produced are in a tractable preceramic polymer compositionhaving either an Mn greater than about 10,000 D, an Mw greater thanabout 16,000 D, an Mz greater than about 40,000 D, a polysilazanespecies having a molecular weight higher than about 50,000 D, orcombinations thereof.
 8. A method of preparing silazanes and siloxazanessuitable as preceramic polymers, comprising the steps of:(a) providing alinear, branched or cyclic starting material having the structure --R'₂Si--A-- in its molecule, in which A is hydrogen, NR, or Si and whereinsaid starting material is oligomeric, polymeric or copolymeric; (b)providing a transition metal catalyst effective to activate Si--N,Si--Si and/or Si--H bonds; and (c) reacting the starting material in thepresence of such catalyst with (1) hydrogen or a hydrogen donor where Ais NR and the starting material is part of a silazane or (2) H--X--Rwhere A is hydrogen or Si, wherein: the R groups are independentlyselected from the group consisting of: hydrogen; boryl; hydrocarbylincluding lower alkyl, alkenyl, alkynyl, aryl, lower alkyl substitutedaryl, cycloaliphatic; silyl or polysilyl; said hydrocarbyl or silyloptionally substituted with amino, hydroxyl, an ether moiety or an estermoiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms,or an organometallic radical; the R' moieties are independently selectedfrom the group consisting of: hydrogen; amino; hydrocarbyl includinglower alkyl, alkoxy, alkenyl, alkynyl, aryl, lower alkyl substitutedaryl, cycloaliphatic; silyl or polysilyl; said hydrocarbyl or silyloptionally substituted with amino, hydroxyl, an ether moiety or an estermoiety, lower alkoxy, or a fused aromatic radical of 8 to 20 carbonatoms, and wherein R and R' may be part of an oligomeric or polymericstructure; and X is selected from the group consisting of NR, NR--NR,and NR--R--NR.
 9. The method of claim 8, wherein the starting materialis of the following structures, where x is an integer from 0 to 4inclusive, y is an integer from 0 to 4 inclusive, z is an integer from 0to 2 inclusive, the sum of x, y and z is 4, a and b are integers from 0to 2 inclusive, the sum of a and b is 2, and m is an integer definingthe number of monomer units in the oligomer, polymer or copolymer.##STR37##
 10. The method of claim 8, wherein the starting material is ofthe formula R'_(a) SiH_(b) wherein a is an integer from 0 to 2inclusive, b is an integer from 2 to 4 inclusive, and the sum of a and bis
 4. 11. The method of claim 1, wherein said reaction is of type (b),said one or more reactants includes a siloxane, and said silazaneproducts include siloxazanes.